Additive manufacturing with heat-flexed material feeding

ABSTRACT

In additive manufacturing, a composite build material filament and a release material filament are dropped from respective spools to a print head. Each of the composite build material filament and the release material filament includes a metal or ceramic powder plus a binder. On the spools and over the drop height, the filaments are heated to a temperature that flexes the filaments but does not soften them to a breaking point. The drop height is of similar linear scale to the build plate. The materials are debound and sintered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional application Ser. No. 62/430,902, filed Dec. 6, 2016,entitled “WARM SPOOL FEEDING FOR SINTERING ADDITIVELY MANUFACTUREDPARTS”; 62/442,395 filed Jan. 4, 2017, entitled “INTEGRATED DEPOSITIONAND DEBINDING OF ADDITIVE LAYERS OF SINTER-READY PARTS”; 62/480,331filed Mar. 31, 2017, entitled “SINTERING ADDITIVELY MANUFACTURED PARTSIN A FLUIDIZED BED”; 62/489,410 filed Apr. 24, 2017, entitled “SINTERINGADDITIVELY MANUFACTURED PARTS IN MICROWAVE OVEN”; 62/505,081 filed May11, 2017, entitled “RAPID DEBINDING VIA INTERNAL FLUID CHANNELS”;62/519,138 filed Jun. 13, 2017, entitled “COMPENSATING FORBINDER-INTERNAL STRESSES IN SINTERABLE 3D PRINTED PARTS”; 62/545,966filed Aug. 15, 2017, entitled “BUBBLE REMEDIATION IN 3D PRINTING OFMETAL POWDER IN SOLUBLE BINDER FEEDSTOCK”; and 62/575,219 filed Oct. 20,2017, entitled “3D PRINTING INTERNAL FREE SPACE WITH A SINTERABLE POWDERFEEDSTOCK”, the disclosures of which are herein incorporated byreference in their entireties.

FIELD

Aspects relate to three dimensional printing of composite metal orceramic materials.

BACKGROUND

“Three dimensional printing” as an art includes various methods forproducing metal parts.

In 3D printing, in general, unsupported spans as well as overhanging orcantilevered portions of a part may require removable and/or solubleand/or dispersing supports underneath to provide a facing surface fordeposition or to resist deformation during post-processing.

SUMMARY

According to a first aspect of the embodiments of the present invention,a method of additive manufacturing may include dropping a build materialfilament, including a first binder and more than 50% by volume ofsinterable powdered metal, over a drop height from a first spool to aprint head assembly. A release material filament, including a secondbinder and a powdered ceramic, may also be dropped over the drop heightfrom a second spool to the print head assembly. The build materialfilament is heated on the first spool and along the drop height to atemperature lower than a glass transition temperature of a softeningcomponent of the first binder to flex the build material filament.Layers of the build material are deposited and the release materialabove a build plate, the drop height being substantially equal to orlonger than a diagonal of the build plate. The first binder and thesecond binder are debound with a common solvent to form a brown partassembly including each of the build material and the release material.The brown part assembly is sintered while decomposing the releasematerial to a release powder.

Optionally, the build material filament dropped along the drop heighthas a bend radius of more than 10 cm over the drop height. The buildplate may be heated by a build plate heater to 50-120 degrees C.Alternatively, or in addition, the build plate may be positioned belowthe drop height, and the build material may be heated along the dropheight to assisted by convection heat rising from the heated buildplate.

Optionally, the first binder includes a polymer in addition to thesoftening component, and the softening component includes asolvent-extractable non-polymer component selected from a wax, a fattyacid, a fatty acid ester, a fatty alcohol, an alkane, a petrolatum, anaphthalene, a glycol, and a glycerol.

Further optionally, the print head assembly may be laterally transportedto traverse a print area of more than 50% of the surface area of thebuild plate, so that the build material filament is unwound from thefirst spool by the lateral transporting of the print head assembly. Thebuild material filament may be guided with a flexible Bowden tubeleading to the print head assembly, the flexible Bowden tube being lessthan ⅓ of the drop height.

According to another aspect of the embodiments of the present invention,a method of additive manufacturing may include winding a build materialfilament on a first spool, the build material including a first binderand more than 50% by volume of sinterable powdered metal, the windingbeing controlled to be at a first temperature lower than a glasstransition temperature of a softenable component of the first binder andto wind at a bend radius of more than 2 cm. The first spool may betransported at uncontrolled ambient temperatures. A build materialfilament may be unwound from the first spool with a first feedmechanism. The first spool and the drawn build material filament may bemaintained in a heated chamber at the second temperature higher thanroom temperature but lower than a glass transition temperature of asoftenable component of the first binder. Layers of the release materialmay be deposited, and layers of the build material deposited upon theprior deposition of the release material. At least a portion of thefirst binder may be debound to form a brown part assembly including thebuild material. The brown part assembly may be sintered.

Optionally, a free span of the build material filament hangs between thespool and the first feed mechanism, the free span having a bend radiusof more than 10 cm.

Optionally, layers of the build material may be deposited above a buildplate heated by a build plate heater to 50-120 degrees C., wherein thefree span is substantially equal to or longer than a diagonal of thebuild plate. Alternatively, or in addition, the build plate may bepositioned below the free span, and the free span heated to the secondtemperature assisted by convection heat rising from the heated buildplate.

Further optionally, the first spool may be positioned vertically abovethe free span and the build plate, and the first spool heated to thesecond temperature assisted by convection heat rising from the heatedbuild plate.

Alternatively, or in addition, first feed mechanism may be transportedtogether with a print head traversing a print area of more than 50% ofthe surface area of the build plate, so that the build material filamentis unwound from the first spool by the first feed mechanism and by thelateral transporting of the first feed mechanism.

Optionally, the build material filament may be guided with a flexibleBowden tube leading to the first feed mechanism, the flexible Bowdentube being less than ⅓ of the free span.

The build material filament may have a cross sectional diameter morethan 0.5 mm but less than 2 mm, two examples being equal to or less thansubstantially 1 mm (with a flexing temperature greater than 40 degreesC.) and equal to or less than substantially 2 mm, and with a flexingtemperature is greater than 50 degrees C. and less than substantially 55degrees C.

Accordingly, a composite build material filament and release materialfilament (each a composite of metal/ceramic powder plus binder) may bedropped from respective spools to a print head. On the spools and overthe drop height, the filaments may be heated to a temperature thatflexes the filaments but does not soften them to a breaking point, e.g.,heated but below a glass transition temperature of a softener (forexample, wax) of the binder. The drop height may be of similar linearscale to the build plate. The materials may be debound and sintered.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured part mayinclude forming a shrinking or densification linking platform ofsuccessive layers of composite, the composite including a metalparticulate filler in a debindable matrix. The debindable matrix mayinclude different components so as to be a one or two stage binder.Shrinking or densification linking supports are formed of the samecomposite above the shrinking platform. A desired part of the samecomposite is formed upon the shrinking platform and shrinking supports,substantially horizontal portions (e.g., overhangs, bridges, largeradius arches) of the desired part being vertically supported by theshrinking platform (e.g., directly, via the shrinking supports, or via arelease layer). A sliding release layer may be formed below theshrinking platform of equal or larger surface area than a bottom of theshrinking platform (e.g., as shown in FIG. 4) that reduces lateralresistance between the shrinking platform and an underlying surface(e.g., such as a build platform or a tray for sintering). The matrix isdebound sufficient to form a shape-retaining brown part assembly (e.g.,including a sparse lattice of remaining binder to hold the shape)including the shrinking platform, shrinking supports, and desired part.The shape-retaining brown part assembly formed from the same compositeis heated to shrink all of the shrinking platform, the shrinkingsupports, and the desired part together at a same rate as neighboringmetal particles throughout the shape-retaining brown part assemblyundergo atomic diffusion. According, uniform shrinking and the slidingrelease layer reduce distortion.

An apparatus of similar advantage may include a print head that depositsthe shrinking platform, the shrinking supports, and the desired part, asecond printhead that forms the sliding release layer, a debinding washthat debinds the shape-retaining brown part assembly, and a sinteringoven to heat and shrink the shrinking platform, the shrinking supports,and the desired part together at a same rate. Optionally, an open cellstructure including interconnections among cell chambers is deposited inat least one of the shrinking platform, the shrinking supports, and thedesired part; and a fluid debinder is penetrated into the open cellstructure to debind the matrix from within the open cell structure.Additionally, or alternatively, the shrinking platform, shrinkingsupports, and desired part may be formed to substantially align acentroid of the combined shrinking platform and connected shrinkingsupports with the centroid of the part. Further additionally or in thealternative, the shrinking supports may be interconnected to a side ofthe desired part by forming separable attachment protrusions of the samecomposite between the shrinking supports and the side of the desiredpart. Still further additionally or in the alternative, a lateralsupport shell may be formed of the same composite following a lateralcontour of the desired part, and the lateral support shell may beconnected to the lateral contour of the desired part by formingseparable attachment protrusions of the same composite between thelateral support shell and the desired part.

Further optionally, soluble support structures of the debindable matrixmay be formed, without the metal particulate filler, that resistdownward forces during the forming of the desired part, and the matrixdebound sufficient to dissolve the soluble support structures beforeheating the shape-retaining brown part assembly. Alternatively, or inaddition, soluble support structures of a release composite may beformed, the release composite including a ceramic particulate filler andthe debindable matrix, the soluble support structures resisting downwardforces during the forming of the desired part. Before heating theshape-retaining brown part assembly, the matrix may be deboundsufficient to form a shape-retaining brown part assembly including theshrinking platform, shrinking supports, and desired part, and todissolve the matrix of the soluble support structures.

Additionally, or in the alternative, the underlying surface may includea portable build plate. In this case, the shrinking platform may beformed above the portable build plate, and the sliding release layerformed below the shrinking platform and above the portable build platewith a release composite including a ceramic particulate and thedebindable matrix. The shape-retaining brown part assembly may besintered during the heating. The build plate, sliding release layer, andshape-retaining brown part assembly may be kept together as a unitduring the debinding and during the sintering. After sintering, thebuild plate, sliding release layer, shrinking platform, and shrinkingsupports may be separated from the desired part.

Optionally, part release layers may be formed between the shrinkingsupports and the desired part with a release composite including aceramic particulate filler and the debindable matrix, and theshape-retaining brown part assembly sintered during the heating. Thepart release layers and shape-retaining brown part assembly may be kepttogether as a unit during the debinding and during the sintering. Aftersintering, separating the part release layers, shrinking platform, andshrinking supports may be separated from the desired part. In this case,an open cell structure including interconnections among cell chambers inthe shrinking supports may be deposited, and a fluid debinder may bepenetrated into the open cell structure to debind the matrix from withinthe open cell structure.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured partincludes depositing, in successive layers, a shrinking platform formedfrom a composite, the composite including a metal particulate filler ina debindable matrix, and depositing shrinking supports of the samecomposite and above the shrinking platform. An open cell structureincluding interconnections is deposited among cell chambers in theshrinking supports. From the same composite, a desired part is depositedupon the shrinking platform and shrinking supports. The shrinkingplatform, shrinking supports, and desired part are exposed to a fluiddebinder to form a shape-retaining brown part assembly. The fluiddebinder is penetrated into the open cell structure to debind the matrixfrom within the open cell structure. The shape-retaining brown partassembly is sintered to shrink at a rate common throughout theshape-retaining brown part assembly.

Optionally, a sliding release layer is deposited below the shrinkingplatform of equal or larger surface area than a bottom of the shrinkingplatform that reduces lateral resistance between the shrinking platformand an underlying surface. Additionally, or in the alternative, partrelease layers are deposited between the shrinking supports and thedesired part with a release composite including a ceramic particulatefiller and the debindable matrix, and the part release layers andshape-retaining brown part assembly are kept together as a unit duringthe exposing and during the sintering. After sintering, the part releaselayers, shrinking platform, and shrinking supports are separated fromthe desired part. Further optionally, as shown in, e.g., FIGS. 8-10,vertical gaps without release composite are formed between shrinkingsupports and the desired part where a vertical surface of a shrinkingsupport opposes an adjacent wall of the desired part.

Alternatively, or in addition, as shown in, e.g., FIGS. 8-10, a lateralsupport shell block is deposited having a large cell interior, havingcells with cell cavities wider than a thickest wall within the lateralsupport shell block, to assist in diffusing and penetrating debindingfluid into the support. Further alternatively, or in addition, theshrinking supports may be interconnected to a side of the desired partby forming separable attachment protrusions of the same compositebetween the shrinking supports and the side of the desired part.

Further optionally, as shown in, e.g., FIGS. 8-10, a lateral supportshell of the same composite as the shrinking supports may be depositedto follow a lateral contour of the desired part. In this case, thelateral support shell may be connected to the lateral contour of thedesired part by forming separable attachment protrusions of the samecomposite between the lateral support shell and the desired part.Alternatively, or in addition, at least one of the shrinking platform,the lateral support shell and the desired part may be deposited withinterconnections between internal chambers, and a fluid debinder may bepenetrated via the interconnections into the internal chambers to debindthe matrix from within the open cell structure. The shrinking platform,shrinking supports, and desired part may be deposited to substantiallyalign a centroid of the combined shrinking platform and connectedshrinking supports with the centroid of the part.

According to another aspect of the embodiments of the present invention,a method of reducing distortion in an additively manufactured partincludes depositing, in successive layers, a shrinking platform formedfrom a composite, the composite including a metal particulate filler ina debindable matrix. Shrinking supports of the same composite may bedeposited above the shrinking platform. As shown in, e.g., FIGS. 8-10,among the shrinking supports, parting lines as separation clearances maybe formed dividing the shrinking supports into fragments separable alongthe separation clearances. From the same composite, a desired part maybe shaped upon the shrinking platform and shrinking supports. The matrixmay be debound sufficient to form a shape-retaining brown part assemblyincluding the shrinking platform, shrinking support columns, and desiredpart. The shape-retaining brown part assembly may be sintered to shrinkat a rate uniform throughout the shape-retaining brown part assembly.The shrinking supports may be separated into fragments along theseparation clearances, and the fragments may be separated from thedesired part.

Optionally, one or more separation clearances are formed as verticalclearance separating neighboring support columns and extending forsubstantially an height of the neighboring support columns, and furthercomprising, and the neighboring support columns are separated from oneanother along the vertical clearances. Alternatively, or in addition,within a cavity of the desired part, interior shrinking supports areformed from the same composite. Among the interior shrinking supports,parting lines may be formed as separation clearances dividing theinterior shrinking supports into subsection fragments separable alongthe separation clearances. The subsection fragments may be separatedfrom one another along the separation clearances.

Alternatively, or in addition, the fragments are formed as blocksseparable from one another along a separation clearance contiguouswithin a plane intersecting the shrinking supports. A lateral supportshell of the same composite as the shrinking supports may be formed tofollow a lateral contour of the desired part. Optionally, the lateralsupport shell may be connected to the lateral contour of the desiredpart by forming separable attachment protrusions of the same compositebetween the lateral support shell and the desired part. Furtheroptionally, in the lateral support shell, parting lines may be formeddividing the lateral support shell into shell fragments separable alongthe parting lines. The matrix may be debound sufficient to form ashape-retaining brown part assembly including the shrinking platform,shrinking support columns, lateral support shell, and desired part. Thelateral support shell may be separated into the shell fragments alongthe parting lines. The shell fragments may be separated from the desiredpart.

Further optionally, at least one of the shrinking platform, theshrinking supports, and the desired part may be deposited withinterconnections between internal chambers, and a fluid debinderpenetrated via the interconnections into the internal chambers to debindthe matrix from within the open cell structure. Alternatively, or inaddition, soluble support structures of the debindable matrix withoutthe metal particulate filler may be formed that resist downward forcesduring the forming of the desired part, and the matrix deboundsufficient to dissolve the soluble support structures before sinteringthe shape-retaining brown part assembly.

Still further optionally, a sliding release layer may be formed belowthe shrinking platform of equal or larger surface area than a bottom ofthe shrinking platform that reduces lateral resistance between theshrinking platform and build plate, and the shrinking platform may beformed above the portable build plate. The sliding release layer may beformed below the shrinking platform and above the portable build platewith a release composite including a ceramic particulate and thedebindable matrix, the build plate, sliding release layers andshape-retaining brown part assembly may be kept together as a unitduring the debinding and during the sintering.

Further alternatively or in addition, part release layers may be formedbetween the shrinking supports and the desired part with a releasecomposite including a ceramic particulate filler and the debindablematrix, and the part release layers and shape-retaining brown partassembly may be kept together as a unit during the debinding and duringthe sintering. After sintering, the part release layers, shrinkingplatform, and shrinking supports may be separated from the desired part.

According to another aspect of the embodiments of the present invention,in a method for building a part with a deposition-based additivemanufacturing system, a polymer-including material is deposited along afirst contour tool path to form a perimeter path of a layer of the greenpart and to define an interior region within the perimeter path. In asecond direction retrograde the first direction, the material isdeposited based on a second contour tool path to form an adjacent pathin the interior region adjacent the perimeter path, The deposition ofthe adjacent path in the second direction stresses polymer chains in thematerial in a direction opposite to stresses in polymer chains in thematerial in the perimeter path, and reduces part twist caused byrelaxation of the polymer chains in the part.

Optionally, one of a start of deposition or a stop of deposition isadjusted to be located within the interior region of the layer. Furtheroptionally, the locations of the start point and the stop point definean arrangement selected from the group consisting of an open-squarearrangement, a closed-square arrangement, an overlapped closed-squarearrangement, an open-triangle arrangement, a closed-trianglearrangement, a converging-point arrangement, an overlapped-crossarrangement, a crimped-square arrangement, and combinations thereof.Alternatively, or in addition, a contour tool path between the startpoint and the stop point further defines a raster path that at leastpartially fills the interior region.

According to another aspect of the embodiments of the present invention,in a method for building a part with a deposition-based additivemanufacturing system having a deposition head and a controller, a firsttool path for a layer of the part is received by the controller, whereinthe received first tool path comprises a perimeter contour segment. Asecond tool path for a layer of the part is received by the controller,wherein the received second tool path comprises an interior regionsegment adjacent the perimeter contour segment. A deposition head ismoved in a pattern that follows the perimeter contour segment of thereceived first tool path to produce a perimeter path of a debindablecomposite including sinterable powder; and moving the deposition head ina pattern that follows the interior region segment of the receivedsecond tool path to produce an interior adjacent path of the debindablecomposite, wherein the perimeter path and the adjacent path aredeposited in directions so that directions of residual stress within abinder of the debindable composite are opposite in the perimeter pathand the adjacent path.

According to still another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system, a digital solid model (e.g., 3D mesh or3D solid) of the part is received, and the digital solid model is slicedinto a plurality of layers. A perimeter contour tool path is generatedbased on a perimeter of a layer of the plurality of layers, wherein thegenerated perimeter contour tool path defines an interior region of thelayer. An interior adjacent path is generated based on the perimetercontour tool path within the interior region. A debindable composite isextruded including sinterable powder in a first direction based on theperimeter contour tool path to form a perimeter of the debindablecomposite for the layer. The debindable composite is extruded in asecond direction based on the perimeter contour tool path to form aninterior adjacent path of the debindable composite for the layer,wherein the deposition of the perimeter contour tool path and theinterior adjacent path are traced in retrograde directions to oneanother so that directions of residual stress within a binder of thedebindable composite are opposite in the perimeter contour tool path andthe interior adjacent path. Optionally, a start point of the perimetercontour tool path and a stop point of the perimeter contour tool pathare adjusted to locations within the interior region.

According to still another aspect of the embodiments of the presentinvention, in method for building a part with an deposition-basedadditive manufacturing system having a deposition head and a controller,a first tool path for a layer of the part is received by the controller,wherein the received first tool path comprises a contour segment. Asecond tool path for a layer of the part is received by the controller,and the received second tool path may overlap the first tool path overat least 90 percent of a continuous deposition length of the second toolpath. The deposition head is moved in a pattern that follows the firsttool path to produce a perimeter path of a debindable composite for thelayer. The deposition head is moved in a pattern that follows the secondtool path in a retrograde direction to the first tool path to produce astress-offsetting path adjacent the perimeter path of debindablecomposite, such that directions of residual stress within a binder ofthe debindable composite are opposite in the perimeter path and thestress-offsetting path. Optionally, the second tool path is continuouslyadjacent at least 90 percent of the first tool path within the samelayer, and comprises an interior region path. Further optionally, thesecond tool path is continuously adjacent over at least 90 percent ofthe first tool path within an adjacent layer, and comprises a perimeterpath of the adjacent layer.

According to yet another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system having an deposition head and acontroller, a tool path is generated with a computer. Instructions forthe generated tool path are transmitted to the controller, and adebindable composite is deposited from the deposition head while movingthe deposition head along the generated tool path to form a perimeterpath of a layer of the part. The perimeter path may include a firstcontour road portion, and a second contour road portion, each of thefirst contour road portion and the second contour road portion crossingone another with an even number of X-patterns, forming an even number ofconcealed seams for the layer.

According to yet another aspect of the embodiments of the presentinvention, in a method for building a part with a deposition-basedadditive manufacturing system having a deposition head and a controller,the deposition head is moved along a first tool path segment to form aperimeter road portion for a layer of the part, and is moved along adirection changing tool path segment. The deposition head may be movedalong a second tool path segment to form a stress-balancing road portionadjacent to the perimeter road portion. Optionally, the directionchanging tool path segment is a reflex angle continuation between thefirst tool path segment and the second tool path segment within the samelayer. Further optionally, a debindable composite including a binder anda sinterable powder is deposited in a first direction about a perimeter.An interior path is deposited along the perimeter in a directionretrograde the first direction. The deposition of the adjacent pathstresses long-chain molecules in the binder in a direction opposite tostresses in the perimeter path, and reduces part twist during sinteringcaused by relaxation of the long-chain molecules in the part.

According to yet another aspect of the embodiments of the presentinvention, in a method of depositing material for additivemanufacturing, a composite material is fed including a binder matrix anda sinterable powder. Successive layers of a wall of a part are depositedto form a first access channel extending from an exterior of the part toan interior of the part. Successive layers of honeycomb infill in theinterior of the part are deposited to form a distribution channelconnecting an interior volume of the honeycomb infill to the firstaccess channel. The binder matrix is debound (e.g., dissolved) byflowing a debinding fluid through the first access channel and thedistribution channel within the interior volume of the honeycomb infill.

Optionally, successive layers of the wall of the part are deposited toform a second access channel extending from the exterior of the part tothe interior of the part, and the binder matrix is debound by flowing adebinding fluid in through the first access channel, via thedistribution channel, and out through the second access channel. Furtheroptionally, the first access channel is connected to a pressurizedsupply of debinding fluid to force debinding fluid through the firstaccess channel, distribution channel, and second access channel.Alternatively, or in addition, successive layers of honeycomb infill aredeposited in the interior of the part to form a plurality ofdistribution channels connecting an interior volume of the honeycombinfill to the first access channel, at least some of the plurality ofdistribution channels being of different length from other of thedistribution channels.

According to another aspect of the embodiments of the present invention,in a method of depositing material for additive manufacturing, a metalmaterial including a binder matrix and sinterable powdered metal havingan average particle diameter lower than 8 micrometers are fed, the metalmaterial having a first sintering temperature. A ceramic material is fedincluding a same binder matrix and a sinterable powdered ceramic, theceramic material including a mixture of a first ceramic having a highersintering temperature than the metal material with a second ceramichaving a lower sintering temperature than the metal material, theceramic material substantially matching a shrinking behavior of themetal material and having a second sintering temperature substantiallyin a same range as the first sintering temperature. Layers of the metalmaterial are formed by deposition upon a prior deposition of layers ofthe metal material, and layers of the metal material are formed bydeposition upon prior deposition of layers of the ceramic material. Atleast a portion of the binder matrix is debound from each of the metalmaterial and ceramic material. A part so formed from the metal materialand ceramic material is heated to the first sintering temperature,thereby sintering the first material and the second material. Successivelayers of a wall of a part are deposited to form a first access channelextending from an exterior of the part to an interior of the part, aswell as to form a distribution channel connecting an interior volume ofthe honeycomb infill to the first access channel. A binder matrixretaining sinterable powder is debound by flowing a debinding fluidthrough the first access channel and the distribution channel within theinterior volume of the honeycomb infill.

According to a further aspect of the embodiments of the presentinvention, in method of depositing material to form a sinterable brownpart by additive manufacturing, a first filament feeding along amaterial feed path, the first filament including a binder matrix andsinterable spherized and/or powdered first material having a firstsintering temperature. A green layer of first material is formed bydeposition upon a brown layer of first material. At least a portion ofthe binder matrix is debound from each green layer of first material todebind each green layer into a corresponding brown layer. Following theformation of substantially all brown layers of the part, the part may besintered at the first sintering temperature.

In an alternative, or in addition, in a method of depositing material toform a sinterable brown part by additive manufacturing, a first filamentis fed including a binder matrix and sinterable spherized and/orpowdered first material having a first sintering temperature. A secondfilament is fed including a second material having a second sinteringtemperature more than 300 degrees C. higher than the first sinteringtemperature. Layers of second material are formed by deposition upon abuild plate or prior deposition of first or second material. Greenlayers of first material are formed by deposition upon prior depositionof a brown layer or second material, and at least a portion of thebinder matrix from each green layer of first material is debound, todebind each green layer into a corresponding brown layer. Following theformation of substantially all brown layers of the part, the part may besintered at the first sintering temperature but below the secondsintering temperature, thereby sintering the first material withoutsintering the second material.

According to another aspect of the embodiments of the present invention,in a method of sintering a brown part article formed from a powderedsinterable material, a brown part integrally formed from a first powderhaving a first sintering temperature in a powder bed is placed within acrucible, the powder bed including a second powder having a secondsintering temperature more than 300 degrees C. higher than the firstsintering temperature. The second powder is agitated to fill internalcavities of the brown part. A weight of an unsupported portion of thebrown part is continually resisted with the second powder. The brownpart is sintered at the first temperature without sintering the secondpowder to form a sintered part. The sintered part is removed from thepowder bed.

Optionally, the agitating includes fluidizing the second powder byflowing a pressurized gas into the bottom of the crucible.Alternatively, or in addition, the weight of an unsupported portion ofthe brown part is continually resisted with the second powder, at leastin part by maintaining a buoyant force having an upward component in thefluidized second powder.

According to another aspect of the embodiments of the present invention,in a method of fabricating a 3D printed from a powdered sinterablematerial, a first filament is fed including a binder matrix andsinterable spherized and/or powdered first material having a firstsintering temperature. A second filament is fed including a secondmaterial having a second sintering temperature more than 300 degrees C.higher than the first sintering temperature. Layers of second materialare formed by deposition upon a build plate or a prior deposition offirst or second material, and green layers of first material are formedby deposition upon prior deposition of a brown layer or second material.At least a portion of the binder matrix from each green layer of firstmaterial is debound, to debind each green layer into a correspondingbrown layer. The part is placed integrally in a powder bed within acrucible, the powder bed including a third powder having a thirdsintering temperature more than 300 degrees C. higher than the firstsintering temperature. The third powder is agitated to fill internalcavities among the brown layers, and a weight of an unsupported portionof the brown layers is continually resisted with the third powder. Thepart is sintered at the first temperature without sintering the thirdpowder to form a sintered part, and the sintered part is removed fromthe powder bed.

According to another aspect of the embodiments of the present invention,in a method for additive manufacturing, a material is suppliedcontaining a removable binder and greater than 50% volume fraction of apowdered metal having a melting point greater than 1200 degrees C., inwhich more than 50 percent of powder particles of the powdered metalhave a diameter less than 10 microns. The material is additivelydepositing in successive layers to form a green body, and the binder isthen removed to form a brown body. The brown part or body is loaded intoa fused tube formed from a material having an operating temperature lessthan substantially 1200 degrees C., a thermal expansion coefficientlower than 1×10-6/° C. and a microwave field penetration depth of 10 mor higher. The fused tube is sealed and internal air is replaced with asintering atmosphere. Microwave energy is applied outside the sealedfused tube to the brown part. The brown part is sintered a temperaturelower than 1200 degrees C.

According to a further aspect of the embodiments of the presentinvention, in a method for additive manufacturing, a material issupplied containing a removable binder and greater than 50% volume of apowdered metal having a melting point greater than 1200 degrees C., inwhich more than 50 percent of the powder particles have a diameter lessthan 10 microns. The material is additively deposited with a nozzlehaving an internal diameter smaller than 300 microns. The binder isremoved to form a brown body or part. The brown part or body is loadedinto a fused tube formed from a material having a thermal expansioncoefficient lower than 1×10-6/° C. The fused tube is sealed, andinternal air replaced with a sintering atmosphere. Radiant energy isapplied from outside the sealed fused tube to the brown part. The brownpart or body is sintered at a temperature higher than 500 degrees C. butless than 1200 degrees C.

According to a further aspect of the embodiments of the presentinvention, in a method for additive manufacturing, a first brown partmay be supplied formed from a first debound material including a firstpowdered metal, in which more than 50 percent of powder particles of thefirst powdered metal have a diameter less than 10 microns. A secondbrown part may be supplied formed from a second debound materialincluding a second powdered metal, in which more than 50 percent ofpowder particles of the second powdered metal have a diameter less than10 microns. In a first mode, the first brown part may be loaded into afused tube formed from a material having a thermal expansion coefficientlower than 1×10-6/° C., and a temperature inside the fused tube may beramped at greater than 10 degrees C. per minute but less than 40 Cdegrees C. per minute to a first sintering temperature higher than 500degrees C. and less than 700 degrees C. In a second mode, the secondbrown part may be loaded into the same fused tube, and a temperatureinside the fused tube may be ramped at greater than 10 degrees C. perminute but less than 40 degrees C. per minute to a second sinteringtempering temperature higher than 1000 degrees C. but less than 1200degrees C.

Optionally, in the first mode, a first sintering atmosphere isintroduced into the fused tube including inert Nitrogen being 99.999% orhigher free of Oxygen. Further optionally, in the second mode, a secondsintering atmosphere comprising at least 2%-5% (e.g., 3%) Hydrogen maybe introduced into the fused tube. Optionally, the fused tube is formedfrom a fused silica having a microwave field penetration depth of 10 mor higher, and microwave energy is applied to the first and/or secondmaterial brown parts within the fused tube, raising the temperature ofsame. Microwave energy may alternatively, or in addition applied to, toraising the temperature of, susceptor material elements placed outsidethe fused tube and outside any sintering atmosphere within the fusedtube.

In these aspects, optionally, the material is additively deposited at alayer height substantially ⅔ or more of the nozzle width. Optionally, amaterial is supplied in which more than 90 percent of powder particlesof the powdered metal have a diameter less than 8 microns. Furtheroptionally, microwave energy is applied from outside the sealed fusedtube to susceptor material members arranged outside the sealed fusedtube. Microwave energy may be the radiant energy applied from outsidethe sealed fused tube to the brown part. Susceptor material membersarranged outside the sealed fused tube may be resistively heated.Optionally, a temperature inside the fused tube may be ramped at greaterthan 10 degrees C. per minute but less than 40 degrees C. per minute.The material of the fused tube may be amorphous fused silica, and thesintering atmosphere may comprise at least 2% Hydrogen and no more than5% Hydrogen (e.g., 3% Hydrogen). The powdered metal may be a stainlesssteel or a tool steel. The susceptor material may be one of SiC orMoSi2.

According to an additional aspect of the embodiments of the presentinvention, a multipurpose sintering furnace, includes a fused tubeformed from a fused silica having a thermal expansion coefficient lowerthan 1×10-6/° C., and a seal that seals the fused tube versus ambientatmosphere. An internal atmosphere regulator is operatively connected toan interior of the fused tube to apply vacuum to remove gases within thefused tube and to introduce a plurality of sintering atmospheres intothe fused tube, and heating elements are placed outside the fused tubeand outside any sintering atmosphere within the fused tube. A controlleris operatively connected to the heating elements and the internalatmosphere regulator, the controller in a first mode sintering firstmaterial brown parts within a first sintering atmosphere at firstsintering temperature higher than 500 degrees C. and less than 700degrees C., and in a second mode sintering second material brown partswithin a second sintering atmosphere at a second sintering temperaturehigher than 1000 degrees C. but less than 1200 degrees C.

Optionally, the internal atmosphere regulator is operatively connectedto an interior of the fused tube to introduce a first sinteringatmosphere comprising inert Nitrogen being 99.999% or higher free ofOxygen. Further optionally, the controller in the first mode sintersbrown parts primarily formed with Aluminum powder in which more than 50percent of powder particles have a diameter less than 10 microns, withinthe first sintering atmosphere comprising inert Nitrogen being 99.999%or higher free of Oxygen, at the first sintering temperature higher than500 degrees C. and less than 700 degrees C. Alternatively, or inaddition, the controller in the second mode sinters brown partsprimarily formed with Steel powder in which more than 50 percent ofpowder particles have a diameter less than 10 microns, within the secondsintering atmosphere comprising at least 3% Hydrogen, at the secondsintering temperature higher than 1000 degrees C. and less than 1200degrees C.

The controller may ramp a temperature inside the fused tube at greaterthan 10 degrees C. per minute but less than 40 degrees C. per minute.The internal atmosphere regulator may be operatively connected to aninterior of the fused tube to introduce a second sintering atmospherecomprising at least 3% Hydrogen. The controller may ramping atemperature inside the fused tube at greater than 10 degrees C. perminute but less than 40 degrees C. per minute. The fused silica tube maybe formed from a fused silica having a thermal expansion coefficientlower than 1×10-6/° C. and a microwave field penetration depth of 10 mor higher, and wherein the heating elements further comprise a microwavegenerator that applies energy to, and raises the temperature of, thefirst and/or second material brown parts within the fused tube.Susceptor material heating elements may be placed outside the fused tubeand outside any sintering atmosphere within the fused tube, wherein themicrowave generator applies energy to, and raises the temperature of,one or both of (i) the first and/or second material brown parts withinthe fused tube and/or (ii) the susceptor material heating elements. Theheating elements further comprise susceptor material heating elementsplaced outside the fused tube and outside any sintering atmospherewithin the fused tube. A small powder particle size (e.g., 90 percent ofparticles smaller than 8 microns) of metal powder embedded in additivelydeposited material may lower a sintering temperature of stainless steelsto below the 1200 degree C. operating temperature ceiling of a fusedsilica tube furnace, permitting the same silica fused tube furnace to beused for sintering both aluminum and stainless steel (with appropriateatmospheres), as well as the use of microwave heating, resistantheating, or passive or active susceptor heating to sinter bothmaterials.

According to an another aspect of the embodiments of the presentinvention, in a composite material including >50% metal or ceramicspheres, and optionally with a two stage binder, a spool of filamentmaterial is wound and unwound at a temperature higher than roomtemperature but less than a glass transition temperature of a bindermaterial, e.g., 50-55 degrees Celsius. It may be transported in at roomtemperature. Upper spools in a model material chamber may include themodel material and the release material. The spools may be kept in ajoint heated chamber which keeps the spools at the 50-55 degrees Celsiuscontemplated by this example. A build plate may be heated by a buildplate heater to similar or higher temperature (e.g., 50-120 degrees C.)during printing. The heating of the build plate may help maintains thetemperature within the printing compartment at a level above roomtemperature.

Optionally, each spool of material may be kept in its own independentchamber. A heater for maintaining the spool temperature may be passive,e.g., radiant and convection heater, or include a blower. Heated air maybe driven through Bowden tubes or other transport tubes through whichthe filament material is driven. The spools may be vertically arrangedon a horizontal axle, and the filament dropped substantially directlydown to the moving printing heads so as to have a large bend radius inall bends of the filament. The material may be maintained with no bendmore of smaller than a 10 cm bend radius, and/or no bend radiussubstantially smaller than that of the spool radius).

According to an another aspect of the embodiments of the presentinvention, in a method for 3D printing green parts, a binder is jettedonto successive layers of powder feedstock to form a 2D layer shape ofbound powder per layer. A 3D shape is additively deposited (e.g., builtup) of a desired 3D green part from interconnected 2D layer shapes ofthe bound powder. A 3D shape of sintering supports is additivelydeposited (e.g., built up) from interconnected 2D layer shapes of thebound powder, and a 3D shape of a shrinking platform is additivelydeposited (e.g., built up) from interconnected 2D layer shapes of thebound powder. A release material is additively deposited (e.g., builtup) upon shapes of bound powder to form 2D layer shapes of releasematerial, and a 3D shape of release surfaces additively deposited (e.g.,built up) from interconnected 2D layer shapes of the release material. Aplaceholder material is additively deposited (e.g., built up) uponshapes of bound powder to form 2D layer shapes of placeholder material,and a 3D shape of placeholder volumes is additively deposited (e.g.,built up) from interconnected 2D layer shapes of the placeholdermaterial. The bound powder, release material, and placeholder materialare debound to form a green part assembly including the desired 3D greenpart, the sintering supports, the release surfaces, and internalcavities corresponding to the 3D shapes of the placeholder materialbefore debinding.

According to this aspect, for 3D printing green parts to be debound andsintered, a binder may be jetted into successive layers of sinterablepowder feedstock to build up a 3D shape of a desired 3D green part,associated sintering supports, and an associated shrinking platform. Arelease material may be deposited to intervene between the 3D greenparts and the sintering supports. A placeholder material may bedeposited upon bound powder to form 2D layer shapes of placeholdermaterial, and the sinterable powder feedstock refilled and leveled aboutthe placeholder material. Upon debinding, internal cavitiescorresponding to the 3D shapes of the placeholder material are formed.

According to an another aspect of the embodiments of the presentinvention, an apparatus for additive manufacturing by depositingsinterable powdered metal in a soluble binder include a nozzle assembly,including a nozzle body within which is formed a first centralcylindrical cavity of substantially constant diameter and a nozzleoutlet connected to the cylindrical cavity, the nozzle outlet being of0.1-0.4 mm diameter. A heat break member abuts the nozzle assembly, theheat break member including a heat break body having a narrowed waistportion, a second central cylindrical cavity of substantially constantdiameter being formed through the heat break body and narrowed waistportion. A melt chamber is formed shared by the first and second centralcylindrical cavity, the melt chamber being of 15-25 mm{circumflex over( )}3 volume and 1 mm or less in diameter.

According to an another aspect of the embodiments of the presentinvention, a 3D printer may deposit, from the powdered metal (orceramic) and binder composites discussed herein, a densification linkingplatform that is equal to or larger than a lateral or horizontal extentof a desired part, e.g., a minimum size that corresponds to the envelopeof the part, at least partially separated from the part by a ceramicrelease layer. The thickness of the densification linking platformshould be at least ½ mm-10 mm thick such that the forces developedduring the shrinking process from atomic diffusion in the raftsubstantially counteract the friction force between the brown bodyassembly and a plate or carrier upon which sintering is performed. Thedesired part may be optionally tacked to the densification linkingplatform with small-cross sectional area (e.g., less than ⅓ mm diameter)connections of the metal composite material that penetrate the ceramicrelease layer vertically in order to ensure that the part shrinks in thesame geometric manner as the densification linking platform that it isresting on. The densification linking platform is optionally formedhaving a cross-sectional area in the shape of a convex shape (a polygonor curved shape without concavities), and/or in a symmetric shape havinga centroid aligned with that of the part above. The densificationlinking platform tends to densify and shrink in a regular or predictablemanner due to its simple geometry, and if as the desired part isconnected to the raft it decreases geometry specific part distortionthat arises from the friction forces between the desired part and thedensification linking platform, especially in the case of asymmetricparts, parts with high aspect ratio cross sections, and parts withvariable thicknesses. The number and placement of tack points betweenthe part and the raft may be selected such that the raft can be suitablyremoved after the sintering process. Optionally, vertical walls outsidethe perimeter of the part that are solidly attached to the densificationlinking may extend at least partially up the sides of the desired partto further reduce distortion. These vertical supports may also beseparated from the desired by the ceramic release layer.

It is expressly contemplated that the foregoing examples of aspects ofembodiments of the present invention, when combined individually or inmultiple combinations, form additional examples of aspects ofembodiments of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic representation of three-dimensional metalprinter.

FIG. 1B is a schematic representation of a three-dimensional metalprinter, representing a binder jetting/powder bed printing approach.

FIG. 2 is a block diagram and schematic representation of a threedimensional printer system.

FIG. 3 is a flowchart describing the overall operation of the 3D printerof FIG. 2.

FIG. 4 is a schematic representation of a 3D printing system, part, andprocess in which sintering supports (e.g., shrinking or densificationlinking supports) are provided.

FIGS. 5A-5D are schematic sections through the diagram of FIG. 4.

FIG. 6 is a schematic representation of an alternative 3D printingsystem, part, and process to that of FIGS. 4 and 5A-5D.

FIG. 7 is a schematic representation of one exemplary process ofprinting, debinding, sintering, and support removal with separationand/or release layers, green body supports and/or sintering or shrinkingor densification linking supports.

FIG. 8 is a schematic representation of an additional alternative 3Dprinting system, part, and process to that of FIG. 4.

FIG. 9 is a schematic representation of an additional alternative 3Dprinting system, part, and process to that of FIG. 4.

FIG. 10 is a top view of a sintered assembly of the 3D printing system,part, and process of FIG. 4, showing parting lines for removing supportshells or sintering or shrinking supports.

FIG. 11 is a top view of a sintered assembly of an alternative 3Dprinting system, part, and process to that of FIG. 4, showing partinglines for removing support shells or sintering or shrinking supports.

FIGS. 12 and 13 are, respectively, orthogonal and 3D/orthographic viewsof the part schematically depicted FIGS. 8 and 9.

FIGS. 14-16 are schematic views of a 3D printer in which filamentmaterials are configured in environmental conditions suitable forprinting.

FIG. 17 is a depiction of elastic modulus vs. temperature showing anappropriate range for maintaining a sinterable additive manufacturingfeedstock in a filament to permit spooling and transportation.

FIGS. 18-21 are schematic views of a 3D printers in which debinding maytake place as each layer is printed, or following each layer or a set oflayers.

FIG. 22 is a flowchart showing a method of depositing material to form asinterable brown part by additive manufacturing.

FIGS. 23A and 23B are alternative schematic representations of analternative 3D printing system, part, and process to that of FIGS. 4and/or 6.

FIG. 24 is a schematic representation of one exemplary process ofprinting, debinding, sintering, and support removal optionally withseparation and/or release layers, green body supports and/or fluidizedbed sintering.

FIG. 25 is a schematic representation of an additional exemplary processof sintering optionally with certain configurations of material andsintering oven.

FIG. 26A and FIG. 26B correspond to FIGS. 5B and 5D, respectively, andshow alternative selected sections through FIG. 4 for the purpose ofdiscussing printing and other process steps.

FIG. 26C and FIG. 26D are examples of respectively, hexagonal andtriangular honeycombs shown in cross section and employed as infill.

FIGS. 27 and 28 show side sectional views, substantially similar indescription to FIGS. 4, 6, 8 and 9, in which honeycomb cavities/infillare formed as vertical, columnar prism shapes.

FIG. 29 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, and 28 in which the distributionchannels cavities/infill are formed in an aligned, and/or angled, mannerthroughout the columnar prism shapes.

FIGS. 30 and 31 show a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, 28 and 29, in which access channelsare provided.

FIG. 32 shows a chart in which the amount of shrinkage of the ceramicsintering support material should be less than that of the part modelmaterial until the final shrinkage amount is reached.

FIGS. 33A-33D, exaggerated in scale, show part shapes including eitheror both of convex or concave shapes (protrusions, cavities, orcontours).

FIGS. 34A and 34B show a flowchart and schematic, respectively, of agravity-aided debinding process useful with parts as described herein.

FIG. 35 shows a 3D printer for forming green parts from a curable ordebindable photopolymer.

FIGS. 36A and 36B show schematics representing deposition direction ofdeposition paths in retrograde patterns.

FIGS. 37A-37H, 37J are schematic views representing seam and jointinteraction in deposition walls and honeycombs.

FIGS. 38A and 38B show FDM/FFF nozzle assemblies in cross section.

FIGS. 39A and 39B show a MIM material extrusion nozzle assemblies incross-section.

FIG. 40 shows a MIM material extrusion nozzle assembly in cross-section.

DETAILED DESCRIPTION

This patent application incorporates the following disclosures byreference in their entireties: U.S. Patent Application Ser. Nos.61/804,235; 61/815,531; 61/831,600; 61/847,113; 61/878,029; 61/880,129;61/881,946; 61/883,440; 61/902,256; 61/907,431; and 62/080,890; Ser.Nos. 14/222,318; 14/297,437; and 14/333,881, may be referred to hereinas “Composite Filament Fabrication patent applications” or “CFF patentapplications”. Although the present disclosure discusses various metalor ceramic 3D printing systems, at least the mechanical and electricalmotion, control, and sensor systems of the CFF patent applications maybe used as discussed herein. In addition, U.S. Pat. Nos. 6,202,734;5,337,961; 5,257,657; 5,598,200; 8,523,331; 8,721,032, and U.S. PatentPublication No. 20150273577, are incorporated herein by reference intheir entireties. Further, U.S. Patent Application Ser. Nos. 62/429,711,filed Dec. 2, 2016; 62/430,902, filed Dec. 6, 2016; 62/442,395, filedJan. 4, 2017; 62/480,331, filed Mar. 31, 2017; 62/489,410, filed Apr.24, 2017; 62/505,081, filed May 11, 2017; 62/519,138, filed Jun. 13,2017; 62/545,966, filed Aug. 15, 2017; 62/575,219, filed Oct. 20, 2017;and Ser. No. 15/722,445, filed Oct. 2, 2017 include related subjectmatter and are incorporated herein by reference in their entireties.

In 3D printing, in general, overhanging or jutting portions of a partmay require removable and/or soluble and/or dispersing supportsunderneath to provide a facing surface for deposition. In metalprinting, in part because metal is particularly dense (e.g., heavy),removable and/or soluble and/or dispersing supports may also be helpfulto prevent deformation, sagging, during mid- or post-processing—forexample, to preserve shape vs. drooping or sagging in potentiallydeforming environments like high heat.

Printing a sinterable part using a 3D printing material including abinder and a ceramic or metal sintering material is aided by supportstructures that are able to resist the downward pressure of, e.g.,extrusion, and locate the deposited bead or other deposition in space. Arelease layer intervening between the support structures and the partincludes a higher melting temperature material—ceramic or hightemperature metal, for example, optionally deposited with a similar(primary) matrix or binder component to the model material. The releaselayer does not sinter, and permits the part to “release” from thesupports. Beneath the release layer, the same model material as the partis used for the support structures, promoting the samecompaction/densification during sintering. This tends to mean the partand the supports will shrink uniformly, maintaining dimensional accuracyof the part. At the bottom of the support, a release layer may also beprinted. In addition, the support structures may be printed in sectionswith release layers between the sections, such that the final sinteredsupport structures will readily break into smaller subsections for easyremoval, optionally in the presence of mechanical or other agitation. Inthis way, a large support structure can be removed from an internalcavity via a substantially smaller hole. In addition, or in thealternative, a further method of support is to print soluble supportmaterial that is removed in the debinding process. For catalytic debind,this may be Delrin (POM) material.

One method to promote uniform shrinking or densification is to print aceramic release layer as the bottom most layer in the part. On top ofthe sliding release layer (analogous to microscopic ball bearings) athin sheet of metal—e.g., a raft—may be printed that will uniformlyshrink with the part, and provide a “shrinking platform” or“densification linking” platform to hold the part and the relatedsupport materials in relative position during the shrinking ordensification process. Optionally staples or tacks, e.g., attachmentpoints, connect and interconnect (or link as densification linking) themodel material portions being printed.

The printer(s) of FIGS. 1A, 1B, and otherwise shown in the remainingdrawings through FIG. 40, with at least two print heads 18, 10 and/orprinting techniques, deposits with one head a composite materialincluding a binder and dispersed spheres or powder 18 (e.g., withinthermoplastic or curing binder), used for printing both a part andsupport structures, and with a second head 18 a (shown in FIGS. 4-9)deposits the release or separation material. Optionally a third headand/or fourth head include a green body support head 18 b and/or acontinuous fiber deposition head 10. A fiber reinforced compositefilament 2 (also referred to herein as continuous core reinforcedfilament) may be substantially void free and include a polymer or resinthat coats, permeates or impregnates an internal continuous single coreor multistrand core. It should be noted that although the print head 18,18 a, 18 b are shown as extrusion print heads, a “fill material printhead” 18, 18 a, 18 b as used herein may include optical or UV curing,heat fusion or sintering, or “polyjet”, liquid, colloid, suspension orpowder jetting devices—not shown—for depositing fill material, so longas the other functional requirements described herein are met.Functional requirements include one or more of employing green bodymaterial supports printing vs. gravity or printing forces; sintering orshrinking (densification linking) supports the part vs. gravity andpromote uniform shrinking via atomic diffusion during sintering; andrelease or separation materials substantially retain shape throughdebinding stems but become readily removable, dispersed, powderized orthe like after sintering.

Although FIGS. 1A, 1B through 40 in general show a Cartesian arrangementfor relatively moving each print head in 3 orthogonal translationdirections, other arrangements are considered within the scope of, andexpressly described by, a drive system or drive or motorized drive thatmay relatively move a print head and a build plate supporting a 3Dprinted part in at least three degrees of freedom (i.e., in four or moredegrees of freedom as well). For example, for three degrees of freedom,a delta, parallel robot structure may use three parallelogram armsconnected to universal joints at the base, optionally to maintain anorientation of the print head (e.g., three motorized degrees of freedomamong the print head and build plate) or to change the orientation ofthe print head (e.g., four or higher degrees of freedom among the printhead and build plate). As another example, the print head may be mountedon a robotic arm having three, four, five, six, or higher degrees offreedom; and/or the build platform may rotate, translate in threedimensions, or be spun. The print bed or build plate, or any other bedfor holding a part, may be moved by 1, 2, or 3 motors in 1, 2, or 3degrees of freedom.

A long or continuous fiber reinforced composite filament is fullyoptional, and when used, is fed, dragged, and/or pulled through aconduit nozzle optionally heated to a controlled temperature selectedfor the matrix material to maintain a predetermined viscosity, force ofadhesion of bonded ranks, melting properties, and/or surface finish.After the matrix material or polymer of the fiber reinforced filament issubstantially melted, the continuous core reinforced filament is appliedonto a build platen 16 to build successive layers of a part 14 to form athree dimensional structure. The relative position and/or orientation ofthe build platen 16 and print heads 18, 18 a, 18 b, and/or 10 arecontrolled by a controller 20 to deposit each material described hereinin the desired location and direction. A driven roller set 42, 40 maydrive a continuous filament along a clearance fit zone that preventsbuckling of filament. In a threading or stitching process, the meltedmatrix material and the axial fiber strands of the filament may bepressed into the part and/or into the swaths below, at times with axialcompression. As the build platen 16 and print head(s) are translatedwith respect to one another, the end of the filament contacts an ironinglip and be subsequently continually ironed in a transverse pressure zoneto form bonded ranks or composite swaths in the part 14.

With reference to FIG. 1A, 1B through 40, each of the printheads 18, 18a, 18 b, 10 may be mounted on the same linear guide or different linearguides or actuators such that the X, Y motorized mechanism of theprinter moves them in unison. As shown, each extrusion printhead 18, 18a, 18 b may include an extrusion nozzle with melt zone or meltreservoir, a heater, a high thermal gradient zone formed by a thermalresistor or spacer (e.g., stainless steel, glass, ceramic, optionally anair gap), and/or a Teflon or PTFE tube. A 1.75-1.8 mm; 3 mm; or largeror smaller thermoplastic (and/or binder matrix) filament is driven via,e.g., a direct drive or a Bowden tube drive, and provides extrusion backpressure in the melt reservoir.

FIG. 1B shows in schematic form a binder jetting powder bed printer,with some components generally similar to the extrusion printer of FIG.1A. The printer 1000J includes two or more print heads 18 (jetting orapplying a binder to bind powder 132 to form model material or boundcomposite), 18 a (jetting or extruding release or separation material),and or 18 b (jetting or extruding placeholder material) supplied bysupply lines 142. The printer 1000J may deposit with print head 18 abinder 132 upon the powder bed 134 to form a composite materialincluding a debinder and dispersed spheres or powder (metal or ceramicpowder), used for printing a part, support structures, and a shrinkingor densification linking platform. A sinterable powder feedstockreservoir, supply or refill 136 supplies the powder bed 134 with newlayers of unbound powder, which is leveled by a leveling or doctor roll138. Excess from leveling is captured in a feedstock overflow reservoir140. With a second head 18 a, the printer 1000J may deposit release orseparation material. Optionally the third head and/or fourth headinclude the placeholder material head 18 b and/or a continuous fiberdeposition head 10 as described herein. The binder jetting printer 1000Jdescribed herein meets the functional requirements described herein(e.g., green body and/or placeholder material supports printing vs.gravity or printing forces, sintering supports support the part vs.gravity and promote uniform shrinking via atomic diffusion duringsintering, and release or separation materials substantially retainshape through debinding steps but become readily removable, dispersed,powderized or the like after sintering).

FIG. 2 depicts a block diagram and control system of the threedimensional printers, e.g., in FIGS. 1A and 1B, which controls themechanisms, sensors, and actuators therein, and executes instructions toperform the control profiles depicted in and processes described herein.A printer is depicted in schematic form to show possible configurationsof e.g., three commanded motors 116, 118, and 120. It should be notedthat this printer may include a compound assembly of printheads 18, 18a, 18 b, and/or 10.

As depicted in FIG. 2, the three-dimensional printer 3001 (alsorepresentative of printer 1000 and 1000J) includes a controller 20 whichis operatively connected to any fiber head heater 715 or similar tipheater, the fiber filament drive 42 and the plurality of actuators 116,118, 120, wherein the controller 20 executes instructions which causethe filament drive 42 to deposit and/or compress fiber into the part.The instructions are held in flash memory and executed in RAM (notshown; may be embedded in the controller 20). An actuator 114 forapplying a spray coat (including a spray release powder), as discussedherein, may also be connected to the controller 20. In addition to thefiber drive 42, respective filament feeds 1830 (e.g., up to one each forheads 18, 18 a, and/or 18 b) may be controlled by the controller 20 tosupply one or more extrusion printheads 18, 18 a, 18 b, 1800. Aprinthead board 110, optionally mounted on the compound printhead andmoving therewith and connected to the main controller 20 via ribboncable, breaks out certain inputs and outputs. The temperature of theironing tip 726 may be monitored by the controller 20 by a thermistor orthermocouple 102; and the temperature of the heater block holding nozzleof any companion extrusion printhead 1800 may be measured by respectivethermistors or thermocouples 1832. A heater 715 for heating the ironingtip 726 and respective heater(s) 1806 for heating respective extrusionnozzles 18, 18 a, 18 b, 1802 are controlled by the controller 20. Heatsink fan(s) 106 and a part fan(s) 108, each for cooling, may be sharedbetween the printheads, or independently provided per printhead, andcontrolled by the controller 20. A rangefinder 15 that measures adistance from the printhead assembly to the part (and thereby a surfaceprofile of the part) is also monitored by the controller 20. The cutter8 actuator, which may be a servomotor, a solenoid, or equivalent, isalso operatively connected to the controller 20. A lifter motor forlifting one or any printhead away from the part (e.g., to controldripping, scraping, or rubbing) may also be controlled by the controller20. Limit switches 112 for detecting when the actuators 116, 118, 120have reached the end of their proper travel range are also monitored bythe controller 20.

As depicted in FIG. 2, an additional breakout board 122, which mayinclude a separate microcontroller, provides user interface andconnectivity to the controller 20. An 802.11 Wi-Fi transceiver connectsthe controller to a local wireless network and to the Internet at largeand sends and receives remote inputs, commands, and control parameters.A touch screen display panel 128 provides user feedback and acceptsinputs, commands, and control parameters from the user. Flash memory 126and RAM 130 store programs and active instructions for the userinterface microcontroller and the controller 20.

FIG. 3 depicts a flowchart showing a printing operation of the printers1000 in FIGS. 1 through 40. FIG. 3 describes, as a coupledfunctionality, control routines that may be carried out to alternatelyand in combination use the co-mounted FFF extrusion head(s) 18, 18 a,and/or 18 b and/or a fiber reinforced filament printing head as in theCFF patent applications.

In FIG. 3, at the initiation of printing, the controller 20 determinesin step S10 whether the next segment to be printed is a fiber segment ornot, and routes the process to S12 in the case of a fiber filamentsegment to be printed and to step S14 in the case of other segments,including e.g., base (such as a raft or shrinking/densification linkingplatform), fill (such as extruded or jet-bound model material, releasematerial, or placeholder material), or coatings (such as sprayed orjetted release material). After each or either of routines S12 and S14have completed a segment, the routine of FIG. 3 checks for slicecompletion at step S16, and if segments remain within the slice,increments to the next planned segment and continues the determinationand printing of fiber segments and/or non-fiber segments at step S18.Similarly, after slice completion at step S16, if slices remain at stepS20, the routine increments at step S22 to the next planned slice andcontinues the determination and printing of fiber segments and/ornon-fiber segments. “Segment” as used herein corresponds to “toolpath”and “trajectory”, and means a linear row, road, or rank having abeginning and an end, which may be open or closed, a line, a loop,curved, straight, etc. A segment begins when a printhead begins acontinuous deposit of material, and terminates when the printhead stopsdepositing. A “slice” is a single layer, shell or lamina to be printedin the 3D printer, and a slice may include one segment, many segments,lattice fill of cells, different materials, and/or a combination offiber-embedded filament segments and pure polymer segments. A “part”includes a plurality of slices to build up the part. Support structuresand platforms also include a plurality of slices. FIG. 3's controlroutine permits dual-mode printing with one, two, or more (e.g., four)different printheads, including the compound printheads 18, 18 a, 18 b,and/or 10. For example, the decision at S10 may be a “case” structurewhich proceeds to different material printing routines in addition toS12, S14.

All of the printed structures previously discussed may be embeddedwithin a printed article during a printing process, as discussed herein,expressly including reinforced fiber structures of any kind, sparse,dense, concentric, quasi-isotropic or otherwise as well as fill material(e.g., including model material and release material) or plain resinstructures. In addition, in all cases discussed with respect toembedding in a part, structures printed by fill material heads 18, 18 a,18 b using thermoplastic extrusion deposition may be in each casereplaced with soluble material (e.g., soluble thermoplastic or salt) toform a soluble preform which may form a printing substrate for partprinting and then removed. All continuous fiber structures discussedherein, e.g., sandwich panels, shells, walls, reinforcement surroundingholes or features, etc., may be part of a continuous fiber reinforcedpart. The 3D printer herein discussed with reference to FIGS. 1-40 maythereby deposit either fill material (e.g., composite with a debindablematrix containing metal, ceramic, and/or fibers), soluble (e.g.,“soluble” also including, in some cases, debindable by thermal,pyrolytic or catalytic process) material, or continuous fiber.

Commercially valuable metals suitable for printing include aluminum,titanium and/or stainless steel as well as other metals resistant tooxidation at both high and low temperatures (e.g., amorphous metal,glassy metal or metallic glass). One form of post-processing issintering. By molding or 3D printing model material as described herein,a green body may be formed from an appropriate material, including abinder or binders and a powdered or spherized metal or ceramic (ofuniform or preferably distributed particle or sphere sizes). A brownbody may be formed from the green body by removing one or more binders(e.g., using a solvent, catalysis, pyrolysis). The brown body may retainits shape and resist impact better than the green body due to remeltingof a remaining binder. In other cases the brown body may retain itsshape but be comparatively fragile. When the brown body is sintered athigh temperature and/or pressure, remaining or second stage binder maypyrolise away, and the brown body substantially uniformly contracts asit sinters. The sintering may take place in an inert gas, a reducinggas, a reacting gas, or a vacuum. Application of heat (and optionally)pressure eliminates internal pores, voids and microporosity between andwithin the metal or ceramic beads through at least diffusion bondingand/or atomic diffusion. Supporting material, either the same ordifferent from model material, supports the part being printed,post-processed, or sintered versus the deposition force of printingitself (e.g., green body supports) and/or versus gravity (e.g., greenbody supports or sintering supports), particularly for unsupportedstraight or low-angle spans or cantilevers.

Printing a part is aided by the support structures, able to resist thedownward pressure of, e.g., extrusion, and locate the deposited bead ordeposition in space. As discussed herein a release layer includes ahigher melting temperature or sintering temperature powderedmaterial—ceramic for example, optionally deposited in or via a similar(primary) matrix component to the model material. Beneath the releaselayer, the same (metal) material is used as the part, promoting the samecompaction/densification. This tends to mean the part and the supportswill shrink uniformly, maintaining overall dimensional accuracy of thepart. At the bottom of the sintering support, a release layer may alsobe printed. In addition, the sintering support structures may be printedsections with release layers, such that the final sintered supportstructures will readily break into smaller subsections for easy removal,optionally in the presence of mechanical or other agitation. In thisway, a large support structure can be removed from an internal cavityvia a substantially smaller hole. In addition, or in the alternative, afurther method of support is to print soluble support material that isremoved in the debinding process. For catalytic debind, this may beDelrin (POM) material. One method to promote uniform shrinking is toprint a ceramic release layer as the bottom most layer in the part. Ontop of the sliding release layer (analogous to microscopic ballbearings) a thin sheet of metal—e.g., a raft—may be printed that willuniformly shrink with the part, and provide a “shrinking platform” or“densification linking platform” to hold the part and the relatedsupport materials in relative position during the shrinking ordensification process. Optionally staples or tacks, e.g., attachmentpoints, connect and interconnect the model material portions beingprinted.

As noted, in one example, green body supports may be printed from athermal, soluble, pyrolytic or catalytically responsive material (e.g.,polymer or polymer blend) and leave behind only removable byproducts(gases or dissolved material) when the green body supports are removed.In another example, green body supports may optionally be printed from amatrix of thermal, soluble, or catalytic debindable composite material(e.g., catalytic including Polyoxymethylene—POM/acetal) and high meltingpoint metal (e.g., molybdenum) or ceramic spheres, and leave behind apowder when debound. The green body supports may be formed to bemechanically or chemically or thermally removed before or afterdebinding, but preferably are also made from thermal, soluble, pyrolyticor catalytically responsive material, and may be fully removed duringthe debinding stage (or immediately thereafter, e.g., subsequent powdercleaning to remove remainder powder). In some cases, the green bodysupports are removed by a different chemical/thermal process from thedebinding, before or after debinding.

An exemplary catalytically debindable composite material including POMor acetal is one example of a two-stage debinding material. In somecases, in a two-stage debinding material, in a first stage a firstmaterial is removed, leaving interconnected voids for gas passage duringdebinding. The first material may be melted out (e.g., wax),catalytically removed (e.g., converted directly into gas in a catalyticsurface reaction), or dissolved (in a solvent). A second stage binder,e.g., polyethylene, that is not as responsive to the first materialprocess, remains in a lattice-like and porous form, yet maintaining theshape of the 3D printed object awaiting sintering (e.g., before themetal or ceramic balls have been heated to sufficient temperature tobegin the atomic diffusion of sintering). This results in a brown part,which includes, or is attached to, the sintering supports. As the partis sintered at high heat, the second stage binder may be pyrolised andprogressively removed in gaseous form.

FIGS. 4 through 7 show, in schematic form, additional explanation ofrelevant processes, structures, materials, and systems. As shown inFIGS. 4-7, a 3D printer 1000 suitable for the deposition phase of theprocess may include one, two, three, or more deposition heads 18, 18 a,18 b for depositing model material and supports (as well as, e.g., acontinuous composite deposition head 10, not shown in FIGS. 4-7). Asshown in FIG. 4, a model material deposition head 18 deposits acomposite material including metal or ceramic spherized powder as wellas a meltable or matrix of binding polymers, waxes, and/or other utilitycomponents. In the model material deposition head 18, the process mayuse a low-diameter filament (e.g., 1-4 mm) as both material supply andto provide back pressure for extrusion. In this case, the model materialextrusion filament supplied to head 18 may be stiff, yet reasonablypliable as supplied (e.g., 0.1-3.0 GPa flexural modulus) and reasonablyviscous when fluidized (e.g., melt or dynamic viscosity of 100-10,000Pa·s, preferably 300-1000 Pa·s) in order to support bridging whileprinting across gaps or spans, even absent green body supports orsintering (i.e., shrinking or densification linking) supports below.

In the 3D printer 1000 and exemplary part 14 shown in FIG. 4, aseparation or release material deposition head 18-S (or 18 a) and agreen body support material deposition head 18-G (or 18 b, the greenbody support material also or alternatively being a placeholdermaterial) may additionally be supported to move in at least threerelative degrees of freedom with respect to the part P1 being printed asdiscussed with reference to FIGS. 1-3 inclusive. As discussed herein,the separation material may in some cases serve as a green body support,so alternatively, as shown in FIG. 6, only one head 18-SG may depositboth green body support material and separation material. As shown inFIG. 4, from bottom to top (in this case, 3D printing is performed fromthe bottom up), in these exemplary processes the first layer printed isa raft separation layer or sliding release layer SL1 printed from, e.g.,the separation material deposition head 18-S (or 18-SG). The separationmaterial may be, as noted herein, of similar debinding materials to themodel material, but, e.g., with a ceramic or other spherical powderfiller (e.g., particulate) that does not sinter, melt, or otherwiseharden together at the sintering temperature of the model material.Consequently, the separation material may have its debinding materialcompletely removed by solvent, catalysis, pyrolysis, leaving behind adispersible and/or removable powder (e.g., after sintering, the powderof the separation material remaining unsintered even after the sinteringprocess). “Separation” and “release” are generally used interchangeablyherein.

FIGS. 5A-5D show selected sections through FIG. 4 for the purpose ofdiscussing printing and other process steps. It should be noted that theFigures are not necessarily to scale. In particular, very smallclearances or material-filled clearances (e.g., separation or releaselayers) or components (e.g., protrusions for snap removal) may be shownat exaggerated scales for the purpose of clear explanation. Moreover, itshould also be noted that in some cases, solid bodies are shown tosimplify explanation, but the internal structure of the solid bodiesherein may be 3D printed with porous, cellular, or hollow infillpatterns (e.g., honeycombs) and/or may include chopped, short, long, orcontinuous fiber reinforcement as discussed in the CFF PatentApplications.

As shown in FIGS. 4 and 5A, upon an optionally removable andtransportable, optionally ceramic build plate 16, a raft separationlayer SL1 is printed by separation material head 18-S to permit a raftor shrinking platform or densification linking platform RA1 printedabove to be readily removed from the build plate 16, in some casesbefore debinding, or in some cases when the (e.g., portable) build plate16 itself is still attached through the debinding process (in theexample shown in FIG. 7).

As shown in FIGS. 4 and 5B, following the printing of the raftseparation layer SL1, a raft or shrinking platform or densificationlinking platform RA1 of model material (e.g., metal-bearing composite)is printed. The raft or shrinking platform RA1 is printed, e.g., for apurpose of providing a continuous model material foundation or materialinterconnection among the part and its supports, so that the process ofmass transport and shrinking/densification during sintering is uniformlycarried out, e.g., about a common centroid or center of mass, e.g.,“densification linking”. The raft RA1 may serve other purposes—e.g.,improving early adhesion, clearing environmentally compromised (e.g.,wet, oxidized) material from an extrusion or supply path, orconditioning printing nozzles or other path elements (e.g., rollers) toa printing state, etc. As noted, two general classes of supports may beused: green body supports GS1, GS2 (which support the part being printedduring the printing process, but are removed before or during sintering)and sintering (e.g., shrinking or densification linking) supports SS1,SH1, RA1 (which support the part being sintered during the sinteringprocess). Green body support GS2 also may be used to “placehold”internal volumes, either holes or cavities in the part shape itself orinternal honeycomb cavities. Some supports may serve both roles. Asshown in FIGS. 4 and 5B, should an upper portion of the entire printbenefit from green body supports, the lower layers of green bodysupports GS1 may be printed upon either the build plate 16, or as shownin FIGS. 4 and 5B, upon the separation layer SL1 and/or the raft orshrinking platform RA1.

As shown in FIGS. 4 and 5C, subsequently, the raft or shrinking platformRA1 may be continued up into or connected up to a surrounding or lateralshell support structure SH1 (either contiguously or via a parting linePL and/or physical separation structure, e.g., a pinched and/orwasp-waisted and/or perforated or otherwise weakened cross-section thatmay be flexed to break away). Further, separation structures—in thiscase model material protrusions P1 as well as an optionally interveningseparation layer SL2—may be printed between the raft RA1 and shell SH1to permit the removal of the raft RA1 and shell SH1 subsequent tosintering. Protrusions P1 described herein, facing vertical, horizontal,or other direction, may be formed to be snapped by sharp or pulsedimpact(s), e.g., having a contact surface cross-section of less than ½mm. The printing of green body supports GS1 is continued upwards, inthis case providing printing support to optionally angled (e.g., 10-45degrees from vertical), sparse and/or branching sintering (e.g.,shrinking or densification linking) supports SS1 printed to laterprovide sintering support for an overhanging or cantilevered portionOH1, as well as building up a green body support GS1 for printingsupport for the same overhanging or cantilevered portion OH1. “Printingsupport” as used herein may mean support vs. printing back pressure orgravity during printing, while “sintering support” may mean support vs.gravity, support vs. other external/internal stress during sintering, aswell as or alternatively meaning providing interconnections facilitatingevenly distributed mass transport and/or atomic diffusion. Although anoverhanging or cantilevered portion OH1 is show in FIG. 4, anunsupported span contiguous to the part P1 at two opposing sides, mayalso benefit from supports as described.

As shown in FIGS. 4 and 5D, the surrounding shell support structure SH1is continued up printing in layers, and optionally interconnectedvertically or diagonally to the part 14 via, e.g., protrusions P1 ofmodel material connected to the shell support structure SH1, and/orseparation layer material SL2 material. The parting lines and separationstructures similarly are continued vertically, preserving the planesalong which they will be removed. An internal volume V1 in the part P1,in this case a cylindrical volume V1, is printed with green bodysupports GB2—if the model material is sufficiently viscous orshape-retaining during printing, the 3D printing process may bridge gapsor diagonally stack, and internal volumes with sloping walls orarch-like walls may not require sintering supports. Alternatively, theinternal volume V1 is printed with sintering supports, or a combinationof green body supports GB # and sintering supports SS #, e.g., as withthe supports SS1 below overhang OH1. The internal volume V1 is printedwith a channel to the outside of the part to permit support material tobe removed, cleaned away, or more readily accessed by heat transfer orfluids or gasses used as solvents or catalysis. The green body supportsGS1 and branching sintering supports SS1 are similarly continued tolater provide sintering support for an overhanging or cantileveredportion OH1, as well as building up a green body support GS1 forprinting support for the same overhanging or cantilevered portion OH1.

As shown in FIGS. 4 and 5D, an overhang or cantilevered portion OH1 maybe supported by sintering supports SS1 at an angle, so long as thesintering supports SS1 are self-supporting during the printing processe.g., either by the inherent stiffness, viscosity, or other property ofthe model material as it is printed in layers stacking up at a slightoffset (creating the angle), or alternatively or in addition with thelateral and vertical support provided by, e.g., the green body supportsGS1. The sintering supports SS1 must also be robust to remain integralwith the part 14 or supporting the part 14 through the sinteringprocess. Any of the sintering supports SS1 shown in FIG. 5C or 5D mayalternatively be vertical columns or encased by a columnar sinteringsupport encasing structure deposited from model material.

Finally, as shown in FIG. 4, the remainder of the part 14, support shellstructure SH1, sintering (e.g., shrinking or densification linking)supports SS1, and green body supports GS1, GS2 are printed tocompletion. As printed, essentially all portions of the part 14 whichrequire printing or sintering support are supported in a verticaldirection either via green body supports GS1, GS2, sintering (e.g.,shrinking or densification linking) supports SS1, the raft RA1,separation layer SL1 and/or SL2. Portions of the part 14, or structureswithin the part 14 that are self-supporting (because, e.g., of thematerial properties of the model material composite, or external bodiesproviding support, and/or those which are sufficiently stiff duringsupport removal, debinding, and/or sintering) need not be supported vs.gravity. In addition, the support structures SS1, the raft RA1, and/orthe shell structure SH1 are interconnected with model material to thepart 14 in a manner that tends to shrink during sintering about a samecentroid or center of mass or at least maintain relative local scalewith respect to the neighboring portion of the part 14. Accordingly,during the approximately 12-24% (e.g., 20%) uniform shrinking ordensification of the sintering process, these support structures shrinkor densify together with the part 14 and continue to provide support vs.gravity.

FIG. 6 shows a variation of the 3D printer, printing method, partstructure, and materials of FIG. 4. In FIG. 6, no separate green bodysupport deposition head 18 c (or 18-G) is provided. Accordingly, greenbody supports GS1, GS2 and separation layers SL1, S12 are formed fromthe same material—e.g., the composite material used for separationlayers, in which a ceramic or high-temperature metal particles orspheres are distributed in an, e.g., one-stage or two-stage debindablematrix. In this case, the green body supports GS1, GS2 are notnecessarily removed during or before debinding or in a separate process,but are instead simply weakened during debinding and, as with theseparation layers, have their remaining polymer material pyrolizedduring sintering. The remaining ceramic powder can be cleaned out and/orremoved following sintering, at the same time as the separation layers.

FIG. 7 shows one overall schematic of the process. Components in FIG. 7correspond to those of the same appearance labeled in FIG. 4, but arenot labeled in FIG. 7 so that different steps may be shown. Initially,in the 3D printing phase, the part 14, together with its green bodysupports GS, sintering supports SS, and separation layers SL (asdescribed and shown in FIG. 4), is printed in a 3D printer as described.The green body, including all of these support structures (e.g., a greenbody assembly GBA), and optionally still bound or connected to a ceramicor other material build plate 16, is transferred to a debinding chamber(optionally, the debinding chamber is integrated in the 3D printer 1000or vice versa). As noted, if the green body supports are made of adifferent polymer, binder or substance than the first stage debindingmaterial, a separate process may remove the green body supports beforedebinding. If the green body supports are made from either the same orsimilar substances as the first stage debinding material, or one thatresponds to the same debinding process by decomposing or dispersing, thegreen body supports may be removed during debinding. Accordingly, asshown in FIG. 7, debinding includes removing a first binder componentfrom the model material using a thermal process, a solvent process, acatalysis process, or a combination of these, leaving a porous brownbody structure (“DEBINDING”), and may optionally include dissolving,melting, and/or catalyzing away the green body supports (“SUPPORTREMOVAL 1”).

Continuing with FIG. 7, as shown, a brown body (e.g., a brown bodyassembly BBA with the attached sintering support and/or surroundingshell) is transferred to a sintering chamber or oven (optionallycombined with the printer and/or debinding chamber). The brown body,e.g., as a brown body assembly BBA, includes the part, optionally asurrounding shell structure, and optionally sintering supports. Asnoted, the surrounding shell structure and sintering (e.g., shrinking ordensification linking) supports are different aspects of sinteringsupport structure. Optionally, intervening between the shell structureand/or sintering supports are separation layers, formed from, e.g., theseparation material. Optionally, intervening between the shell structureand/or sintering supports are protrusions or ridges of model materialinterconnecting these to the part. Optionally, the same or a similarseparation material intervenes between the brown body (e.g., as brownbody assembly) and the build plate. During sintering, the brown body(e.g., as a brown body assembly) uniformly shrinks by approximately12-24%, such as 20%, closing internal porous structures in the brownbody (e.g., as a brown body assembly) by atomic diffusion. The secondstage debinding component of the model material may be pyrolised duringsintering (including, for example, with the assistance of catalyzing orother reactive agents in gas or otherwise flowable form).

As shown in FIG. 7, a sintered body (e.g., as a sintered body assembly)can be removed from the sintering oven. The supporting shell structureand the sintering supports can be separated or broken up along partinglines, and/or along separation layers, and or by snapping or flexing orapplying an impact to protrusion connections, tacks or otherspecifically mechanically weak structures. The separation layers arepowderized and are readily removed. Should the green body supports beformed from the separation material, the green body supports aresimilarly powderized and may be readily removed.

FIG. 8 shows a variation of a part printed as in FIG. 4 or FIG. 6. Thepart shown in FIG. 8 includes four overhanging or cantilevered sectionsOH2-OH5. Overhang OH2 is a lower, thicker overhang under a cantilevered,thinner overhang OH3. While the lower overhang OH2 may in some cases beprinted without sintering supports or even green-body supports as aself-supporting cantilever, it is below the long cantilever overhangOH3, which is sufficiently long, thin, and heavy that it may requireboth green body supports and sintering supports. Overhang OH4 is adownward-leaning overhang, which generally must be printed with at leastgreen body supports (because its lowest portion is otherwiseunsupported, i.e., in free space, during printing) and in a formdifficult to remove sintering supports printed beneath without draftingor parting lines (because rigid sintering supports would become lockedin). Overhang OH5 is a cantilever including a heavy block of modelmaterial, which may require both green body and sintering support. Inaddition, the part shown in FIG. 8 includes an internal, e.g.,cylindrical volume V2, from which any necessary sintering supports mustbe removed via a small channel. For reference, the 3D shape of the part14 of FIG. 8 is shown in FIGS. 12 and 13.

As shown in FIG. 8, in contrast to the sintering supports SS1 of FIGS. 4and 6, sintering (e.g., shrinking or densification linking) supportsSS2, supporting overhangs OH2 and OH3, may be formed including thinwalled, vertical members. These vertical members form vertical channelswhich, as described herein, may permit fluid flow for debinding. Thevertical members of sintering supports SS2 may be independent (e.g.,vertical rods or plates) or interlocked (e.g., accordion or meshstructures). As shown in FIG. 8, the sintering supports SS2 (or indeedthe sintering supports SS1 of FIGS. 4 and 6, or the sintering supportsSS3, SS4, and SS5 of FIG. 8) may be directly tacked (e.g., “tacked” maybe contiguously printed in model material, but with relatively smallcross-sectional area) to a raft RA2, to the part 14 a, and/or to eachother. Conversely, the sintering supports SS2 may be printed above,below, or beside a separation layer, without tacking. As shown, thesintering supports SS2 are removable from the orthogonal, concavesurfaces of the part 14 a.

Further, as shown in FIG. 8, similar sintering (e.g., shrinking ordensification linking) supports SS3 are printed beneath thedownward-leaning overhang OH4, and beneath heavier overhang OH5. Inorder that these supports SS3, may be readily removed, some or all areprinted with a parting line PL, e.g., formed from separation material,and/or formed from a mechanically weakened separation structure (e.g.,printing with a nearly or barely abutting clearance as described herein,or printing with a wasp-waisted, pinched, or perforated cross-section,or the like), or a combination of these (or, optionally, a combinationof one or both of these with green body support material having littleor no ceramic or metal content, should this be separately printed).These material or mechanical separation structures, facilitating removalof the sintering supports, may be similarly printed into the varioussintering supports shown in FIGS. 4-7, 9, and throughout.

In addition, as shown in FIG. 8, sintering (e.g., shrinking ordensification linking) supports SS5 are printed within the internalvolume V2. The sintering supports SS5 are each provided with multipleparting lines, e.g., printed in a plurality of separable segments, sothat the sintering supports in this case can be broken or fall apartinto parts sufficiently small to be readily removed, via the channelconnecting the internal volume V2. As shown, the channel CH2 itself isnot printed with internal supports, as an example of a small-diameterhole of sufficient rigidity during both printing and sintering to holdits shape. Of course, supports may be printed of either or both types inchannel CH2 to ensure shape retention.

FIG. 9 is substantially similar to FIG. 8, but shows some variations instructure. Both variations in printing with and without reinforcementare shown, e.g., while FIG. 9 shows reinforcement structures CSP1therein, the remaining variant structures in the solid bodies, supports,and separation layers of FIG. 9 are optionally applicable to thenon-reinforced structures of FIG. 8 and throughout. For example, beneathoverhang OH3, a monolithic, form-fitting shell SH3 is printed of modelmaterial, separated from the part 14 by either release or separationlayers SL2 and/or protrusions P1. The monolithic shell SH3 has smallopen cell holes throughout to lower weight, save material, and improvepenetration or diffusion of gases or liquids for debinding. As discussedherein, open cell holes may optionally be connected to access and/ordistribution channels for debinding fluid penetration and draining,e.g., any of the structures of FIGS. 25-31 may form, be formed by or becombined with the open cell holes. This shell SH3 may surround the part14 if sufficient parting lines or release layers are printed into theshell SH3 (e.g., instead of the structures SH4 and SH5 to the left ofthe drawing, a similar structure would be arranged), and if sufficientlyform following, act as a workholding piece.

In another example in FIG. 9, monolithic (e.g., lateral) support (e.g.,shrinking or densification linking) shell SH4 is printed integral withthe raft RA2, but with a parting line PL angled to draft and permitremoval of the support shell SH4. In a further example shown in FIG. 9,support shell SH4 is printed angled upward (to save material) and with alarge cell or honeycomb interior to lower weight, save material, and/orimprove penetration or diffusion of gases or liquids for debinding. FIG.9 also shows examples of continuous fiber layers deposited by, e.g.,continuous fiber head 10. Sandwich-panel reinforcement layers CSP1 arepositioned at various layers, e.g., within upper and lower bounds ofoverhangs OH2, OH3, and OH5.

As shown in FIGS. 4 through 9, sintering supports SS1, SS2, SS3 may beformed in blocks or segments with at least some intervening releaselayer material, so as to come apart during removal. In any of theseFigures and throughout, supports may be tacked or untacked. “Untacked”sintering supports may be formed from the model material, i.e., the samecomposite material as the part, but separated from the part to beprinted by a release layer, e.g., a higher temperature composite havingthe same or similar binding materials. For example, for most metalprinting, the release layer may be formed from a high temperatureceramic composite with the same binding waxes, polymers, or othermaterials. The release layer may be very thin, e.g., one 3D printinglayer. When the metal is sintered, the release layer—having already hada first stage binder removed—is essentially powderized as thetemperature is insufficient to sinter or diffusion bond the ceramicmaterial. This enables the untacked sintering supports to be easilyremoved after sintering.

“Tacked” sintering supports, in contrast, may be similarly formed fromthe model material, i.e., the same composite material as the part, butmay connect to the part either by penetrating the release layer orwithout a release layer. The tacked sintering supports are printed to becontiguous with the part, via thin connections, i.e., “tacked” at leastto the part. The tacked sintering supports may in the alternative, or inaddition, be printed to be contiguous with a raft below the part thatinterconnects the part and the supports with model material. The raftmay be separated from a build plate of a 3D printer by a layer or layersof release layer material.

A role of tacked and untacked of sintering supports is to providesufficient supporting points versus gravity to prevent, or in some casesremediate, sagging or bowing of bridging, spanning, or overhanging partmaterial due to gravity. The untacked and tacked sintering supports areboth useful. Brown bodies, in the sintering process, may shrink byatomic diffusion, e.g., uniformly about the center of mass or centroidof the part. In metal sintering and some ceramics, typically this is atleast in part solid-state atomic diffusion. While there may be somecases where diffusion-based mass transport among the many interconnectedmetal/ceramic spheres does not transport sufficient material to, e.g.,maintain a very thin bridge joining large masses, this is notnecessarily the case with supports, which may be contiguously formedconnected at only one end as a one-ended bridge (or connected at twoends as two-ended bridges; or interconnected over the length).

In those cases where tacked sintering supports are tacked to, orconnected to, or linked to, a model material raft or shrinking platformor densification linking platform upon which the part is printed, theinterconnection of model material among the tacked sintering supportsand the raft can be arranged such that the centroid of the raft-supportscontiguous body is at or near the same point in space as that of thepart, such that the part and the raft-support contiguous to the parteach shrink during sintering uniformly and without relative movementthat would move the supports excessively with respect to the part. Inother cases, the part itself may also be tacked to the model materialraft, such that the entire contiguous body shrinks about a commoncentroid. In another variation, the part is interconnected to the raftvia tacked sintering supports tacked at both ends (e.g., to the raft andto the part) or and/along their length (e.g., to the part and/or to eachother).

In other cases, untacked sintering supports may be confined within avolume and contiguous with the raft and/or the part, the volume formedfrom model material, such that they may shrink about their own centroids(or interconnected centroid) but are continually moved through space andkept in a position supporting the part by the surrounding modelmaterial. For example, this may be effective in the case of the internalvolume V2 of FIG. 8 or 9.

In the alternative, or in addition, support or support structures orshells may be formed from model material following the form of the partin a lateral direction with respect to gravity, e.g., as shown incertain cases in FIGS. 4-9. The model material shells may be printedtacked to the base raft (which may be tacked to the part). They may beprinted integral with, but separable from the base raft. The base raftmay be separable together with the model material shells. These supportstructures may be offset from or substantially follow the lateral outercontours of the part, or may be formed from primitive shapes (straightor curved walls) but close to the part. In one variation, the supportstructures may envelop the part on all sides (in many cases, includingparting lines and/or separation structures to permit the shell to beremoved). These offset support structures may be printed with aseparation layer or layers of the separation material (optionallyceramic or another material that will transfer mechanical support butwill not be difficult to separate).

Any of the support structures discussed herein—e.g., tacked or untackedsintering supports, and/or support shells, may be printed with, insteadof or in addition to intervening separation material, a separationclearance or gap (e.g., 5-100 microns) between the part and supportstructure (both being formed from model material). In this manner,individual particles or spheres of the support structure mayintermittently contact the part during sintering, but as the separationclearance or gap is preserved in most locations, the support structuresare not printed with compacted, intimate support with the part. When andif bonding diffusion occurs at intermittently contacting particles, theseparation force required to remove the separation clearance supportstructures after sintering may be “snap-away” or “tap-away”, and in anycase far lower than an integral or contiguous extension of the part.Larger separation clearances or gaps (e.g., 200-300 microns) may permitdebinding fluid to penetrate and/or drain.

In an alternative, separation gaps or clearances between the part andsupport structures may be placed in partial segments following thecontour, with some of the remainder of the support structures followingthe e.g., lateral contour of the part more closely or more distantly, orboth. For example, support structures may be printed with a smallseparation gap (5-100 microns) for the majority of the supportstructure, but with other sections partially substantially following thecontour printed yet closer to the part (e.g., 1-20 microns) providingincreased rigidity and support during sintering, yet generally over aset of limited contact areas (e.g., less than 5% of contact area),permitting removal. This may also be carried out with large and mediumgaps (e.g., 100-300 microns separation for the larger clearance supportstructures, optionally with separation material intervening, and 5-100microns for the more closely following support structures). Further,this may be carried out in three or more levels (e.g., 100-300 microngaps, 5-100 micron gaps, and 1-20 micron gaps in different portions ofthe support structures following the contour of the part).

Optionally, the sintering support structures may include a followingshell with an inner surface generally offset from the e.g., lateral partcontour by a larger (e.g., 5-300 microns) gap or clearance, but willhave protrusions or raised ridges extending into the gap or clearance toand separated by the smaller gap (e.g., 1-20 microns), or extendingacross the gap or clearance, to enable small point contacts between thepart and support structures formed from the same (or similar) modelmaterial. Point contacts may be easier to break off after sintering thancompacted, intimate contact of, e.g., a following contour shell.Optionally, a neat matrix (e.g., green body supports formed from one ormore of the binder components) support structure may be printed betweenmodel material (e.g., metal) parts and model material (e.g., metal)support structures to maintain the shape of the part and structuralintegrity during the green and brown states, reducing the chance ofcracking or destruction in handling.

While several of the Figures are shown in side, cross section view, FIG.10 shows the sintered body structure of FIG. 4 in top views, while FIG.11 shows a variation for the purpose of explanation. As shown, supportshells or other structures may be printed with separation or partinglines or layers between portions of the support structure. Theseparation or parting lines or layers may be any separation structuredescribed herein, including those described between the part and supportstructure. For example, the separation lines or layer permitting asupport shell to be broken into two or more parts (optionally manyparts) may be formed from separation material (e.g., ceramic andbinder), from binder material, from model material (e.g., metal) withseparation gaps (such as 1-20, 5-100, or 50-300 microns) and/orprotrusions or ridges permitting snap-off structures. For example, asupport structure or shell may be formed to be split in two halves(e.g., as in FIG. 10), creating a parting line in the support structureor shell. Parting lines are optionally printed to be contiguous within aplane intersecting (e.g., bisecting) a support shell structure so as topermit ready separation. Multiple planes of parting lines may intersectthe support shell structure. A “parting line”, “parting surface”, and“parting plane” are used herein similarly to the context in injectionmolding—the plane along which one structure separates from another, forgenerally a similar reason—permitting the part-surrounding structures tobe removed without interference with or entrapment in the part. While inthe context of injection molding these terms refer to the plane alongwhich mold halves separate, in the present disclosure the term “parting”line, surface, or structure refers to the plane along which supportstructures supporting or enveloping a part may break or segment orseparate from one another.

In the case of complex geometries, as noted above, support structuresmay be printed with parting lines, sectioned into smaller subsections(e.g., as PL-1 in FIG. 11, like orange slices, or further sectioned inan orthogonal axis such that they can be easily removed), as shown inFIG. 11. For example, if support structures are printed filling in adovetail of a part, support structures could be formed in three parts,e.g., could be designed in three parts, such that the center part eitherhas draft or is rectangular and can be easily removed, thereby freeingup the two side parts to slide inward and then be removed. Conversely,parting lines may be printed to be interlocking (e.g., PL-3 in FIG. 11),crenellated or formed as a box joint (e.g., similar to PL-3 in FIG. 11),so as to resist separation, in some cases other than in a transversedirection. Parting lines may be printed nearly almost cut through thesupport shell (e.g., PL-2 in FIG. 11). Note that FIG. 11 is depictedwithout protrusions P1, i.e., with only separation layers SL2 in thevertical direction, and largely monolithic, surrounding support shellSH.

In some cases, particularly in the case of a small number of partinglines (e.g., halves, thirds, quarters) the support structures, at leastbecause they are form following structures, may be preserved for lateruse as a workholding fixture, e.g. soft jaws, for holding a sintered thepart in secondary operations (such as machining). For example, if asupport structure were to support a generally spherical part, a supportstructure suitable for later use as a workholding jaw or soft jaw, thestructure should retain the part from all sides, and therefore extendpast the center or half-way point of the sphere. For the purposes ofsintering and supporting vs. gravity, the support structure need notextend past the halfway point (or slightly before), but for the purposesof subsequent workholding for inspection and post processing, thesupport structure would continue past the half way point (e.g. up to ⅔of the part's height, and in some cases overhanging the part) enablingpositive grip in, e.g., a vise.

Further, attachment features to hold the workholding fixture(s) or softjaw(s) in a vise (or other holder) may be added to the support structurefor the purpose of post processing, e.g., through holes for attachmentto a vise, or dovetails, or the like. Alternatively, or in addition, aceramic support may be printed, and sintered, to act as a reusablesupport for the sintering step of many 3D printed parts. In this case,upwardly facing surfaces of the reusable support may be printed toshrink to the same height as the matching or facing surface of the partbeing supported.

As discussed herein, a feedstock material for forming the part and/orthe sintering supports may include approximately 50-70% (preferablyapprox. 60-65%) volume fraction secondary matrix material, e.g.,(ceramic or metal) substantially spherical beads or powder in 10-50micron diameter size, approximately 20-30% (preferably approx. 25%volume fraction of soluble or catalysable binder, (preferably solid atroom temperature), approximately 5-10% (preferably approx. 7-9%) volumefraction of pyrolysable binder or primary matrix material, (preferablysolid at room temperature), as well as approximately 0.1-15% (preferablyapprox. 5-10%) volume fraction of carbon fiber strands, each fiberstrand coated with a metal that does not react with carbon at sinteringtemperatures or below (e.g., nickel, titanium boride). As discussedherein, the “primary matrix” is the polymer binder and is deposited bythe 3D printer, holding the “secondary matrix” beads or spheres and thefiber filler; and following sintering, the (ceramic or metal) materialof the beads or spheres becomes the matrix, holding the fiber filler.

Alternatively, a feedstock material for forming the part and/or thesintering supports may include approximately 50-70% (preferably approx.60-65%) volume fraction secondary matrix material, e.g., (ceramic ormetal) substantially spherical beads or powder in 10-50 micron diametersize, approximately 20-30% (preferably approx. 25% volume fraction ofsoluble or catalysable binder, (preferably solid at room temperature),approximately 5-10% (preferably approx. 7-9%) volume fraction of apyrolysable binder or secondary matrix material approximately 1/10-1/200 the elastic modulus of the (ceramic or metal) secondary matrixmaterial, and approximately 0.1-15% (preferably approx. 5-10%) volumefraction of particle or fiber filler of a material approximately 2-10times the elastic modulus of the secondary, (metal or ceramic) matrixmaterial. As discussed herein, the “primary matrix” is the polymerbinder and is deposited by the 3D printer, holding the “secondarymatrix” beads or spheres and the fiber filler; and following sintering,the (ceramic or metal) material of the beads or spheres becomes thematrix, holding the particle of fiber filler.

A comparison of elastic modulus may be found in the following table,with polymer/binder primary matrices of 1-5 GPa elastic modulus

Secondary Elastic Modulus Elastic Modulus matrix (10⁹ N/m², GPa) Fill(10⁹ N/m², GPa) Steel 180-200 Carbon Fiber 200-600 Aluminum  69 GraphiteFiber 200-600 Copper 117 Boron Nitride 100-400 Titanium 110 BoronCarbide 450 Alumina 215 Silicon Carbide 450 Cobalt 209 Alumina 215Bronze  96-120 Diamond 1220  Tungsten Carbide 450-650 Graphene 1000 Carbon Nanotube 1000+

The spheres, beads or powder (e.g., particulate) may be a range ofsizes. A binder may include dispersant, stabilizer, plasticizer, and/orinter-molecular lubricant additive(s). Some candidate secondarymatrix-filler combinations that may be deposited by a 3D printer withina binder or polymer primary matrix include cobalt or bronze beads withtungsten carbide coated graphite (carbon) fibers; aluminum beads withgraphite (carbon) fibers; steel beads with boron nitride fibers;aluminum beads with boron carbide fibers; aluminum beads with nickelcoated carbon fibers; alumina beads with carbon fibers; titanium beadswith silicon carbide fibers; copper beads with aluminum oxide particles(and carbon fibers); copper-silver alloy beads with diamond particles.Those fibers that may be printed via the techniques of the CFF PatentApplications may also be embedded as continuous fibers. Carbon forms forparticles or fibers include carbon nanotubes, carbon blacks,short/medium/long carbon fibers, graphite flakes, platelets, graphene,carbon onions, astralenes, etc.

Some soluble-pyrolysable binder combinations include polyethylene glycol(PEG) and polymethyl methacrylate (PMMA) (stearic acid optional, PMMA inemulsion form optional); waxes (carnauba, bees wax, paraffin) mixed withsteatite and/or polyethylene (PE); PEG, polyvinylbutyral (PVB) andstearic acid. Some pyrolysable second stage binders include: polyolefinresins polypropylene (PP), high-density polyethylene (HDPE); linearlow-density polyethylene (LLDPE), and polyoxymethylene copolymer (POM).As noted, in thermal debinding, a part containing binder is heated at agiven rate under controlled atmosphere. The binder decomposes by thermalcracking in small molecules that are sweep away by the gas leaving theoven. In solvent debinding, a part containing binder is subject todissolving the binder in appropriate solvent, e.g., acetone or heptane.In catalytic debinding, the part is brought into contact with anatmosphere that contains a gaseous catalyst that accelerates cracking ofthe binder, which can be carried away.

FIG. 14 is a schematic view of a 3D printer in which filament materialsare configured in environmental conditions suitable for printing. Whenbinder materials include at least polymer materials and/or waxes, thebehavior of the polymers and/or waxes for the purposes of feeding andback pressure during printing may be temperature dependent, even at roomtemperature (e.g., 20 degrees C.) and mildly elevated operatingtemperatures (e.g., above 20 degrees C. but below 80 degrees C.). Withincreasing temperature, stiffness decreases and ductility increases.When temperature increases to approach a softening or glass transitiontemperature, elastic modulus changes at a higher rate. For an amorphouspolymer, the elastic modulus and load-bearing ability becomes negligibleabove the glass transition temperature TG-A (as shown in FIG. 17). For asemi-crystalline material, a small amount (e.g., ⅓- 1/10 of elasticmodulus below Tg) of stiffness or elastic modulus may remain mildlyabove the glass transition temperature TG-SC (shown in FIG. 17),continuing to decrease to the melting point. Binder materials—whetherpolymer or wax or both—may have more than one component, and one or moreglass transition temperatures or melting temperatures, and a glasstransition temperature Tg marks a significant softening. FIG. 17 showsone possible spool temperature span for one possible polymer or waxcomponent such as the softening materials discussed herein. However, itshould be noted that the particular position on this curve relative tothe noted glass transition temperature TG of a component is lessimportant than the feeding behavior of the filament as a whole—thefilament should be softened from any brittle state sufficiently to bepulled or drawn off the spool without breaking, yet hard enough to befed by an extruder, and sufficiently pliable to be bent repeatedlywithin the Bowden tubes BT1 and, e.g., cable carrier EC1.

In a composite material including >50% metal or ceramic spheres, as wellas a two stage binder, advantageous mechanical properties for 3Dprinting, debinding and sintering (including melt viscosity, catalyticbehavior and the like) may result in a printing material that—whilehaving properties suitable or advantageous for other parts of theprocess, may be claylike and/or brittle at room temperature, even thoughthe material becomes suitably fluidized but also suitably viscous andself-supporting for 3D printing when at a printing temperature (aboveone or more glass transition temperatures or melting temperatures of thematerial).

Suitable structures for handling materials brittle at room temperatureare shown in FIGS. 14-16, 3D printers schematically depicted andotherwise constructed similarly to FIGS. 1-9. FIGS. 14 and 15 acceptspools of model material and/or release material (as discussed herein,composite material that may be sintered after debinding, or, for releasematerial, that contains high temperature particles or spheres thatresist powderize when a binder portion is pyrolised during sintering)that were wound at a temperature higher than room temperature but lessthan a glass transition temperature of a binder material, e.g., 50-55degrees Celsius, for example with an approximately 1.75 mm diameterfilament. Optionally, the temperature is comparable to the glasstransition or softening temperature of a wax component of the modelmaterial, but lower than the glass transition or softening temperatureof a polymer component. As shown in FIGS. 14 and 16, two upper spoolsinclude the model material and the release material, and these are eachin a joint heated chamber (HC1) heated by a heater HT1. The heater HT1keeps the spools at the 50-55 degrees Celsius contemplated by thisexample, for example with an approximately 1.75 mm diameter filament.The build plate 16 may be heated by a build plate heater 16 a, whichmaintains roughly a similar temperature (e.g., 50-55 degrees Celsius)during printing, and also helps maintains the temperature within theprinting compartment at a level above room temperature. A smallerdiameter filament may be softened sufficient for bending and feeding ata lower temperature (e.g., for a 1 mm filament, 40-45 degrees may beemployed).

Each spool/material may be kept in its own independent chamber ratherthan the joint chamber HC1, and each may be heated by its own heaterrather than the joint heater HT1. Heater HT1 may be a passive, e.g.,radiant and convection heater, or include a blower. As shown in FIGS.14-16, if a return channel RC1 permits air to be drawn into the heatedchamber HC1 from the printing compartment, the blower-type heater maykeep the heated chamber HC1 at a comparative positive pressure. If theheated chamber HC1 is sufficiently sealed except for the return channelRC1 as an inlet and the filament outlets and Bowden tubes BT1 downstreamfrom the driving “extruders” EXT1 (e.g., rubber-wheeled filament drivesystems), the heated air within the heated chamber HC1 may be driventhrough the Bowden tubes BT surrounding the driven filaments to maintainthe temperature at an elevated level as the warmed filament is movedthrough the Bowden tubes and, in some cases, flexed during printing. Atleast the driven air and the heater 16 a heating the build plate maymaintain the printing compartment and the air returned via channel RC1at a higher than room temperature level (and reduce energy consumption).In order that the bending radius of the Bowden tubes, and therefore thefilament inside, are kept controlled, a segmented cable carrier (e.g.,energy chain) that maintains a minimum bending radius EC1 may house theBowden tubes.

FIGS. 14-16 differ in the orientation of the spools and the drivingsystem of the filament. In FIG. 14, spools are horizontally arranged ona lazy-susan type holder that permits rotation, and the filament drivers(including their, e.g., elastomer drive wheels) are arranged at aconvenient location mid-way between the spools and the Bowden tubes.This mid-drive arrangement is suitable if the filament is not softenedto an elastomer range in the heating chamber HC1. In FIG. 15, the spoolsare vertically arranged in a rotating spool holder (e.g., on rollers),and the filament drivers or “extruders” (including their driving wheels,e.g., of elastomer) are arranged directly upstream of the melt chamberin the respective nozzles 18, 18 a. This direct drive arrangement issuitable for softer as well as stiffer filaments. In FIG. 16, the spoolsare vertically arranged on an axle, and the filament, and the filamentdrivers or “extruders” (including their driving wheels, e.g., ofelastomer) are arranged directly upstream of the melt chamber in therespective nozzles 18, 18 a. Moreover, in FIG. 16, the heated chamber isa large volume, and the filament is dropped substantially directly downto the moving printing heads 18, 18 a so as to have a large bend radiusin all bends of the filament (e.g., as shown, no bend more of smallerthan a 10 cm bend radius, or, e.g., no bend radius substantially smallerthan that of the spool radius). Bowden tubes guide the filaments forpart of the height leading up to the spools.

In one alternative embodiment, rather than debinding an entire partafter printing, at least a portion of the debinding is performed whileor after printing layers of the part and/or supports. As discussedherein, debinding may be performed by solvent, heating and/or applyingvacuum evaporation or sublimation, catalysis, or other means of removingor decomposing a binder, in each case removing at least a part of thematrix material for subsequent processes such as sintering. It may bemore advantageous to debind less than a layer at a time (e.g., with adirected debinding head optionally travelling with the print head) or alayer, a few layers, or several layers at a time (e.g., with afull-enclosure debinding system or a region-at-a-time or scannabledebinding system).

Full part molding technologies using debinding, in contrast to additiveor 3D printing technologies, necessarily apply debinding processes to afull molded part. As discussed herein, full part debinding is similarlyuseful for additive or 3D printed parts as well, and may offeradvantages versus molded parts in the case of additive or 3D printedparts (e.g., weight may be reduced and/or debinding accelerated wheninternal honeycomb, access channels, open cells, and other debindingacceleration structures are printed).

In contrast, layer-by-layer debinding (e.g., not limited to one layer ata time—continuous debinding while printing, or debinding part of a layerat a time, or debinding a set of layers are each possible) may haveunique advantages in the case of 3D printed or additive technologies. Aswith molding, a purpose of a first stage binder in the case of extrusion3D printing (e.g., using spooled or coiled filament, spooled or foldabletapes, or feedable rods) is delivery of the sinterable powder into thedesired shape, while a purpose of a second stage binder is adhesion andshape retention in the brown part versus gravity and system/processforces. After delivery, the first stage binder need only be retained solong as is necessary or useful for adhesion and shape retention versusthese forces. In the case of molding, this would be at least until afterthe green part is formed, and in most cases until after the green partis removed from the mold. In the case of 3D printing, depending on thedebinding system and binder material properties, the binder can beremoved substantially immediately after deposition (e.g., if some firststage binder remains, and/or a second stage binder or other componentretains structural integrity versus gravity and printing/processingforces). If sufficient structural integrity remains, a debinding headmay continuously debind “behind” a deposited road that has solidified,or even one that has not yet solidified or cooled to solidification. Asanother example, a debinding head may independently track or scan aportion of a layer, a full layer, or a set of layers; or a volumetric orbulk process (e.g., heating, vacuum) in the printing chamber maycontinuously debind or debind in duty cycles. In all of these cases ofsubstantially layer-by-layer debinding, several advantages result.Significantly, the process of debinding is accelerated because internalsurfaces are directly available for debinding. Similarly, structuresimpractical to debind in full-part process (e.g., dense or large parts)may be debound. No additional time or transport is necessary followingprinting, as the printer continuously transforms (continuously, regionby region, layer by layer, or layer set by layer set) green layers ofthe part into brown layers, and a printed part is a brown part. Evenpartial debinding may accelerate the overall process by increasing theavailable surface area for whole part debinding. For example, a partialdebinding sweep may be conducted upon a printed layer or set of layers,temporarily exposing some surfaces to debinding fluid (gas or liquid).

FIGS. 18-21 are schematic views of a 3D printers in which debinding maytake place as each layer is printed, or following each layer or a set oflayers. The printer of FIGS. 18-21 accept spools of model materialand/or release material that are either temperature controlled to bepliable when heated above room temperature, or are pliable at roomtemperature; or alternatively discrete rod material fed by an, e.g.,piston feeder. The build plate 16 may be heated by a build plate heater16 a, which may maintain a temperature during printing which contributesto debinding (e.g., elevated, but below a fluidizing or softeningtemperature of the model material and may maintains the temperaturewithin the printing compartment at a level above room temperature (theprinting compartment also in addition or alternatively use a separateheater, not shown, for this purpose). As shown in FIGS. 18-21, at leastthe heater 16 a heating the build plate, with the optional assistance ofa chamber heater HT2, may maintain the printing compartment at a higherthan room temperature level, and a segmented cable carrier (e.g., energychain) that maintains a minimum bending radius EC1 may house Bowdentubes as well as air, gas, fluid and/or vacuum lines for fumeextraction.

In one example, as shown in FIG. 18, each of the print heads 180, 180 aincorporates at least a print head (for extruding or spraying modelmaterial, green body support material, or sintering support material)and a debinding head DBH1 (for debinding a first stage binder fromprinted model material). The type of debinding head DBH1 depends uponthe debinding process for the first stage binder material. For example,a debinding head DBH1 for thermally debindable first material mayinclude one or both of a forced hot air gun or a radiant or IR heatelement or projector. In the case of a material debound in a vacuum(increasing a vapor pressure of the binder), the entire chamber may beunder vacuum (e.g., by means of a vacuum pump or high-vacuum apparatusconnected by vacuum conduit VC1) as well; and in the case of a materialdebound in a particular gas (inert or active), the entire chamber may befilled with such gas via inert atmosphere port ATM1. A debinding headDBH1 for a solvent or catalytically debindable first material mayinclude a spray, droplet, or jet of solvent or catalyst fluid, aerosol,or gas (optionally warmed, heated, or recycled). In either case, thedebinding head DBH1 may include or add a waste or fume collection vacuumor extractor FE1. An additional head-borne or whole chamber process mayaccelerate (e.g., by gas flow, vacuum, or heat) removal of the debindingsolvent following the debinding step.

In the case of a heat gun or radiant element, the layer or road of firstmaterial deposited may be heated to temperature of 200-220 degrees C. todebind the material. Optionally, the fume extractor FE1 or vacuum may beconcentric or partially concentric with a heat source, such that fumesare extracted similarly without dependence on the direction of travel ofthe debinding head DBH1. Similarly, the debinding head DBH1, with orwithout the fume extractor FE1, may be concentric with the printing head180 or 180 a, again so that debinding may “follow” or track the printhead 180 or 180 a in any direction, and/or may perform similarly in anyCartesian direction of movement. Alternatively, either of the debindinghead DBH1 or the fume extractor FE1 may be mounted onto a side of theprint head 180 or 180 a (with or without independent articulation fordirection) and may be mounted on a separately or independently movablecarriage. In each case described herein (concentric, adjacent, or mainscan) the fume extractor FE1 is preferably proximate to an output of thedebinding head DBH1 (e.g., spray, heat radiator, etc.), e.g., no morethan 0.1-10 mm from the debinding head DBH1.

Alternatively, as shown in FIG. 19, the debinding head DBH1 is afull-width main scan debinding head, mount on a separate carriage thattravels the width of the printer in a sub scan, and has an optionaltrailing and/or leading fume extractors FE1. This main-scan debindinghead DBH1 may debind the entire layer in one or more passes. The mainscan debinding head DBH1 may be arranged at a predetermined and/oradjustable clearance from each layer, e.g., such that its output (e.g.,heat radiator) faces the part with an, e.g., clearance of 0.1-10 mm, andmay avoid blowing air which may perturb fine printed features.

Further alternatively, as shown in FIG. 20, the debinding head DBH1includes a directable, coherent, or highly collimated radiation beamemitter (e.g., laser) in the debinding head DBH1, fixedly mounted with aline of sight of the useful print bed 16, or on a separate carriage thattravels at least in part to allow line of sight or positioning at anappropriate focus distance; or mounted on the print head DBH1 to movewith it similarly to FIG. 18. A beam emitting debinding head DBH1 maydebind continuously, road by road, or an entire layer in one or morepasses. The preferred power level of the beam or laser may be similar toSLS lasers used for plastic (e.g., 100 mW-100W). In each implementationin FIGS. 18-21 discussed herein, the print bed 16 and/or the chamber maybe elevated by heaters 16 a and/or HT2 to a temperature near thedebinding temperature (e.g., 1-10 degrees below) so that a heat-based orheat-using debinding head DBH1, e.g., beam emitter, need elevate thetemperature of the part layer by only a few degrees in order to performthe debinding process; or may be elevated by heaters 16 a and/or HT2 toa temperature (e.g., 90-150 degrees C.) that partially debinds the layeror continues to debind the layers below the current layer. In eachimplementation in FIGS. 18-21 discussed herein, a warm air jet, ambientair jet or cooled air jet may follow or otherwise track the debindinghead DBH1 to cool the layer following debinding, and/or return it to theoperating temperature of the environment (which may be overall orpartially elevated).

Still further alternatively, as shown in FIG. 21, upon completion of alayer, the part may be lowered (e.g., slightly or completely) into asolvent bath (e.g., circulated, recirculated, agitated and/or heated).In this case, the debinding head DBH1 may be considered the solvent bathstructure; and debinding 1-5 layers at a time may be a more effectiveapproach because of the raising/lowering time. In each example in FIGS.18-21, a fume extractor FE1 may remove dissolved, volatile, atomized,fluidized, aerosolized or otherwise removed binder. The fume extractorFE1 may be connected to a pump which directs the collected material intoa cold trap CT1 (e.g., to condense volatile, sublimated, or gas statematerial to liquid or solid material) and optionally thereafter througha carbon filter or other gas cleaner CF1 before exhausting to anappropriate outlet. A fume extractor FE2 separate from the debindinghead DBH1 may evacuate or remove fumes from the entire chamberseparately.

As shown in FIG. 22, the present disclosure describes a method ofdepositing material to form a sinterable brown part by and an apparatusfor additive manufacturing may include making a raft RA1 in step S40.Subsequently, as discussed herein, in Step S42 a layer, portion of alayer, or set of layers is printed, and in Step S44 the layer is deboundas discussed with reference to FIG. 18-21 and throughout thisdisclosure. This process is repeated—noting that dense printing mayresult in more frequent debinding steps. When all the layers are bothprinted and debound, as in step S46, the process is complete. The methodmay include feeding along a material feed path. The apparatus feeds afirst filament including a binder matrix and sinterable spherized and/orpowdered first material having a first sintering temperature, e.g., themodel material. A green layer of first material is deposited orpartially deposited, at least in some cases upon a brown layer of firstmaterial that has already been debound. In other cases it may bedeposited upon a layer of sintering support or green body supportmaterial. At least a portion of the binder matrix is then removed fromthe green layer or portion thereof of first material to debind eachgreen layer into a corresponding brown layer. When all the green layershave been both printed and converted into brown layers, the part is abrown part and may be sintered the part at the first sinteringtemperature.

When sintering supports are used, the apparatus (and/or process) mayinclude a second print head along a material feed path, and theapparatus can feed a second filament including the binder matrix andsinterable spherized and/or powdered second material having a secondsintering temperature higher than the first sintering temperature(optionally, e.g., more than 300, or more than 500 degrees C. higher).The apparatus forms layers of the second material—the separation layermaterial—which may have a second sintering temperature more than 300degrees C., or more than 500 degrees C. higher than the first sinteringtemperature. Green layers of model material are deposited upon a bydeposition upon a build plate or prior deposition of a brown layer(previously debound layer-by-layer as discussed herein) or separationmaterial, and at least a portion of the binder matrix from each greenlayer is debound to convert that layer or layers into a correspondingbrown layer. Layers of the separation material are deposited upon abuild plate or first or second material, and layers of first material bydeposition upon prior deposition of model material or separationmaterial as appropriate, to permit sintering supports to be laterremoved or build up separation material. When all brown layers of thepart have been so converted, the part may be sintered at the firstsintering temperature but below the second material. The apparatus(including an additional station of the apparatus) debinds at least aportion of the binder matrix from each of the first material and secondmaterial. The apparatus (including an additional station of theapparatus) then heats a part so formed from first and second material tothe first sintering temperature, thereby sintering the first materialwithout sintering and decomposing the second material (the separationmaterial) The second stage binder in the separation material, is,however pyrolized, leaving an unsintered powder behind.

In the present disclosure, a vacuum-assisted debinding process using ahigh vapor pressure first stage binder subject to sublimation (e.g.,naphthalene) may be particularly effective in the case whereinterconnected channels are printed. The 3D printing model material mayinclude a binder and a ceramic or metal sintering material, and arelease layer intervenes between infill cells or honeycomb or open cellsin the part interior that connect to support structures and the partexterior. As discussed herein, open cell holes may optionally form, beformed by, or be connected to access and/or distribution channels fordebinding fluid penetration and draining. “Vacuum-assisted” may meandebinding in gaseous pressure below ambient, optionally below 0.1-5 mmHg, where any remaining gas may be air or inert, with or without addedheat by a debinding head, heated printbed, and/or heatedprinting/debinding chamber. All or some, each of the channels/holes maybe sized to remain open during debinding under vacuum, yet close duringthe approximately 20% size (approximately 20% may be 12-24%) reductionor densification of sintering. In such a case, the first stage bindermay include chemically compatible solid, liquid and/or paste-like higherhydrocarbon and ester binder components having a measurable vaporpressure at the low end of the debinding temperatures (supportstructures and thus readily removable), especially under reducedpressure and elevated temperature conditions, prior to or without theuse of extracting solvents. Preferably, such total or partial waxreplacement components in the binder fraction would be characterized bya low-lying triple point which would make the removal of the componentfeasibly by sublimation, i.e., directly from the solid into the vaporphase, and thus preserving the open structure of the polyolefin binderphase.

In the present disclosure, binder compositions suitable for roomtemperature filament winding, commercial range shipping, and roomtemperature storage and unspooling may be formed by combining lowmelting point waxes and other compatible materials into a first stagebinder. A problem to be overcome is brittleness, which prevents bendingor winding of relatively high-aspect ratio filament (e.g., 1-3 mm)without breaking.

Solvent-debinding MIM feedstocks often include three distinctcomponents. One component is the solvent-extractable partially misciblelower molecular weight component, such as petroleum wax (PW),microcrystalline wax (MW), crystalline wax (CW), bee's wax, C15-C65paraffins and the like. The first stage binder component may serve as apore former that can be rapidly and conveniently removed from the greenpart without changing its dimensions and integrity but that alsofacilitates a controlled and uniform removal of gaseous thermaldecomposition products from the brown part body without deforming it. Asecond component may be a non-extractable, later pyrolized second stagebinder, which may be a thermoplastic polymer selected from variousgrades of polyethylene (PE), such as LDPE, HDPE, LLMWPE, etc.,polypropylene, poly(methyl pentene) or other nonpolar hydrocarbonpolymer. A third component may be a minor fraction of a powderdispersing component, such as long-chain saturated fatty acids (forexample, stearic (SA) or palmitic (PA) acid) that act as disaggregatingsurface active agents for the inorganic or metal powder, alternatively apolar and tacky copoly(ethylene-vinyl acetate) (PEVA) in place of afatty acid as the powder dispersing component.

In these examples, binder compositions may contain a first stage binderof 50-70 vol.-% of hydrocarbon solvent-soluble wax or fatty acidcomponents. In order to be more flexible or pliable in room temperatureor shipping conditions, the first stage binder may include low-meltingbinder components, such as higher alkanes, petrolatum, paraffin waxesand fatty acid esters and other compatible liquid plasticizers toincrease the flexibility of the polymeric binder system. Thesecomponents may improve spool winding on small-diameter spools and toresist impact during handling and shipping (including in colder ambienttemperatures, e.g., below freezing), and may also increase the rate ofextraction during the solvent debinding step.

In one particular example, a measurably volatile plasticizing bindercomponent may have relatively volatility under ambient storage, e.g.,such as naphthalene, 2-methylnaphthalene or another hydrocarbon having atriple point temperature in the vicinity of room temperature as acomponent of a primarily polyolefin binder, or as the majority componentor entire component of a first stage binder. Due to its aromaticity andlow polarity, naphthalene is compatible with a polyethylene (polyolefin)melt and has naphthalene has a relatively very low temperature triplepoint and thus very high vapor pressure over the solid phase up to themelting point at 80 degrees C. In another example, a polyolefin binderis blended with a straight- or branched chain higher (10<n<26) alkane ora mixture of such alkanes, with or without a fraction of naphthalene, inwhich the alkanes or their mixture is selected from compounds having ameasurable vapor pressure at temperatures below the melting point of thepolyolefin or below the dissolution temperature of said polyolefin inthe alkane or its mixture. “Measurable vapor pressure” means a saturatedvapor pressure higher than 0.1 Pa (1 μm Hg) at 20 degrees C.)

The alkane or its mixtures may be replaced in entirety or in part bymono-, di- or triesters of fatty acids and fatty alcohols, glycols orglycerol which also possess a measurable vapor pressure in the rangefrom ambient temperature to the dissolution temperature of thepolyolefin binder in the ester or its mixture. If the alkane, ester orits blend or a blend with a medium-size fatty acid has a measurablevapor pressure at ambient or higher temperature, but below the meltingor dissolution point of the polymer binder, it can conveniently beremoved from the blend by simply exposing the green part to low pressureenvironment, preferable at an elevated temperature, but at leastinitially at a temperature lower than the melting or dissolutiontemperature of the polyolefin binder. The sublimation or evaporation ofthe binder component will generate microporosity in the binder phase ofthe green part, thus facilitating subsequent thermal debinding of thegreen part and preventing its dimensional distortion due to theexpansion of the trapped gaseous decomposition products.

The volatile binder component should have a vapor pressure at ambienttemperature low enough so as not to vaporize to a significant degreeduring normal handling and use of the material in the open atmosphere.Volatile binder loss during long-term storage may be effectivelyprevented by storing the pellets, extruded filament or the like insealed gas- and organic vapor-impermeable multilayer packaging.Polyolefin binders include polyethylene, polypropylene or theircopolymers, as described with a wax component including a proportion ofnaphthalene, 2-methylnaphthalene. Sublimation of naphthalene duringstorage can be prevented by using an appropriate vapor impermeablepackaging material such as an aluminum-polymer laminate, yet naphthalenecan be relatively rapidly removed from the green part by moderateheating under low pressure, for example, in a vacuum oven attemperatures below the melting point of naphthalene and thus remove itwithout melting the binder phase.

As noted, in the case of FIGS. 4-40 inclusive, green body supports areprimarily for supporting the green body vs. printing forces and gravityduring the printing process, and may be removed prior to debindingand/or sintering, while the sintering supports are primarily forsupporting the brown body vs. gravity and for interconnecting supportsto the brown body for uniform shrinking, and are retained through thedebinding process and during the sintering process. The separationmaterial may be debound, and may aid in removal of the sinteringsupports after sintering. In the case of FIG. 6, the green body supportsand separation material may be combined, and the separation material andgreen body supports removed during debinding (some of the powder in theseparation material may remain), while the sintering supports are againretained for supporting the brown body vs. gravity. If it is unnecessaryto support the brown body vs. gravity (e.g., because of buoyancy effectsduring fully submerged sintering in a fluidized bed, or because ofresistance provided by powder underneath, as disclosed herein), then itthe sintering supports may be smaller, not as strong, or evenunnecessary. In this last case, this may be represented by the printingstage of FIGS. 23A and 23B, in which only green body supports/separationmaterial, but not sintering supports, are printed supporting the part.

As shown in FIGS. 23A and 23B, a powder bed or fluidized bed brown partsintering oven and process may be used together with the 3D printersdisclosed herein. The sintering oven shown in FIG. 23A, may be usedtogether with the 3D printers and debinding stations disclosed herein,those in which green body supports and separation layers are formed fromdifferent material, those in which green body supports and separationlayers are formed from the same material, and those in which nosintering supports are formed.

As shown in FIG. 23A, a sintering oven and method may support fluidizedbed sintering of the model material or composite. The release layerincludes a spherized or powder metal part, initially a brown part,during sintering to prevent warping and distortion during the sinteringprocess. For example, the part 23-3 may be placed into a crucible 23-1as shown in FIGS. 23A and 23B. The crucible 23-1 may be partially filledwith a fine powder 23-4 with size from 0.001 microns to 200 microns,preferably with size 1-20 microns. Alternatively, or in addition, if thepowder bed is to be optionally fluidized, the crucible 23-1 may bepartially filled with a powder of Geldart Group A. Geldart Group Apowders are typically substantially between 20 and 100 μm, may bespherical or irregular, and the particle density is optionally less than1.4 g/cm³. However, Geldart Group A powders are defined by bubblingbehavior, not by powder size, and any Geldart Group A powder issuitable. In a Geldart Group A powder, prior to the initiation of abubbling bed phase, beds may expand at incipient fluidization, due todecreased bulk density. Alternatively, a Geldart Group C, or Group B,powder may in some cases be suitable with mechanical or other agitation.

If the powder bed is to be fluidized, pressurized gas appropriate forsintering (e.g., typically an inert gas, or a reducing gas) may enterthe fluidized bed vessel through numerous holes via a distributor plate23-9 or a sparger distributor, the resultant gas-particle fluid beinglighter than air and flowing upward through the bed, causing the solidparticles to be suspended. Heat is applied to the crucible 23-1containing the powder bed (optionally fluidized) and part 23-3. Any partof the system may be appropriately pre-heated, e.g., a pressurized gas23-2 may be pre-heated to a temperature in the below, in the range of,or above the sintering temperature. As the part 23-3 is heated up tosintering temperature, the tendency is to deform downward under gravity,i.e., under the weight of the part 23-3 itself. In the system of FIGS.23A and 23B, the fine powder (preferably alumina, or the like) providesresistance to slumping and sagging, or in other cases, the fluidized bedof fine powder provides either or both of resistance or buoyancy. Thesystem may alternate between fluidized state and a non-fluidized state,and/or the flow rate of the fluid (gas) can further be modulated toachieve varying degrees of powder mobility. As shown, the powder in thebed continually resists weights of unsupported portions of the brownpart (e.g., unsupported portions 23-12).

Optionally, in order to promote flow, and prevent entrapment of powderin orifices and compartments of the part, the powder may besubstantially spherically shaped. Further, the powder bed can befluidized to reduce viscosity through fluid inlet and/or distributorplate 23-9. Further optionally, the crucible 23-1 is positioned in asubstantially gas-tight chamber 23-7 that seals the furnace to preventthe ingress of oxygen—which is usually detrimental to the physicalproperties of metallic powders during the sintering process. Arefractory lining 23-5 is shown, which isolates the high-temperaturecrucible 23-1 from the (preferably stainless steel) walls of thefurnace.

Further optionally, a crucible lid 23-6 may rests on top of the crucible23-1 further limiting oxygen flow into the part 23-3. As the gas flowsinto the crucible 23-1, the pressure may slightly elevate the 23-1 lidto enable gas to escape. The resulting positive pressure flowing gasseal may reduce oxygen ingress, resulting in a more pure atmospherearound the part 23-3. Further optionally, in one embodiment, thefluidizing gas may be maintained at a flow rate below a point ofmobility of the powder during an initial temperature ramp, and throughthe onset of necking among metal powder spheres in the process ofsintering—the initial stages of the sintering process. When sufficientnecking is achieved to connect many spheres and thereby maintain thestructure of the part, the gas flow can be increased to the point offluidizing the powder. Fluidizing (e.g., creating a fluidized bed)during the initial ramp (before necking) may have a destabilizing effecton the part, and may increase the likelihood of cracking or damage.However, once sintering or pre-sintering has enabled sufficient partstrength (e.g., 0.1-10% part shrinkage), and before the part hascontracted to fully sintered (e.g., 12-24%, or approximately 20%shrinkage) fluid flow may be increased to fluidize the support powderwithout damaging the part. Increasing fluid flow later in the processmay require low viscosity powder to ensure egress of powder from holes,cavities and the like.

Further optionally, the properties of the powder, fluid flow, andprinting (including part, supports, and auxiliary structures) may beconfigured to generate buoyancy of the part, on a scale from lowbuoyancy to neutral buoyancy in the fluidized bath. This effectivelyzero gravity sintering process may permit complex shapes with internalspans and bridges to be sintered without sagging or slumping. A mildamount of buoyancy will reduce the effective weight of the part or aportion of the part. However, the buoyancy may be up to neutral (thepart tends to float within the fluidized bed) or above neutral (the parttends to float to the top of the fluidized bed). A supporting hanger23-10 may counteract negative, neutral, or positive buoyancy and holdthe part immersed in the fluidized bed. In addition, a hood guard 23-11shaped to exclude powder directly above the contour of the part mayreduce or eliminate the weight of a hood or stagnant cap ofnon-fluidized powder that may reside above the part. This hood orstagnant cap may reduce overall buoyancy or buoyancy in particularlocations (see, e.g.,https://rucore.libraries.rutgers.edu/rutgers-lib/26379/). The hood guard23-11 may be 3D printed along with the part—e.g., the hood guard 23-11may be determined according to the cross-sectional shape of arepresentative or maximum horizontal section of the part, projectedupward for the expected depth of submersion in the fluidized bed. Thehood guard 23-11 may then be 3D printed as a hollow or substantiallyhollow prism or shell from model material (or sintering supportmaterial), e.g., above the part with a separation layer, or a separateprint job (subsequent or beside the part to be sintered). The hood guard23-11 may also serve the role of a supporting hanger 23-10, and the partmay be suspended via the hood guard 23-11. The hood guard 23-11 may be“sacrificial”, e.g., generated during printing but disposed of orrecycled following sintering.

Further optionally, a gas outlet 8 may allow the exhaust of thesintering process to be removed from the oven. Alternatively, or inaddition, the outlet 8 may be used to pull a vacuum on the furnace(e.g., use a vacuum pump to lower the ambient pressure toward vacuum) toremove a significant portion of the oxygen from the environment prior toflowing the inert or reducing gas for sintering and/or fluidizing thebed. Flowing gas through the powder agitates the powder in addition tofluidizing the powder. Further optionally, a fluidized bed may allow thepart to contract or shrink during sintering without the powder exertingany resistance. While the necessary gas flow to enter a particulateregime and bubbling regime in fluidizing a particular particle size andtype can be well characterized empirically or via modeling, mechanicalagitation, including by stirring members, shaking members or chambers,ultrasonic, magnetic, inductive, or the like may reduce the gas velocityneeded or provide fluidization in more inaccessible sections of thepart.

FIG. 23B shows one overall schematic of the process. Initially, in the3D printing phase, STG-1A the part 14, together with at least its greenbody supports is printed in a 3D printer as described. The green body,including all of these, optionally still bound to a higher meltingtemperature material—ceramic or other material build plate 16, may betransferred to a debinding chamber (optionally, the debinding chamber isintegrated in the 3D printer or vice versa). As noted, green bodysupports may be removed during debinding. Accordingly, as shown in FIG.24, debinding STG-2A debinds the model material, leaving a porous brownbody structure (“DEBINDING”), and may optionally include dissolving,melting, and/or catalyzing away the green body supports (“SUPPORTREMOVAL”). As discussed, sintering supports may remain even with thepowder bed or fluidized powder bed technique, but may be, e.g., placedin fewer locations or support only longer spans.

Continuing with FIG. 23B, as shown, a brown body is transferred to asintering chamber or oven (optionally combined with the printer and/ordebinding chamber). The sintering chamber or oven is filled with apowder, as described, that will not sinter at the sintering temperatureof the brown body (e.g., alumina powder surrounding n aluminum or steelbrown body to be sintered. During sintering STG-3A, the brown bodyuniformly shrinks by approximately 20%, closing internal porousstructures in the brown body by atomic diffusion. The alumina powder beddoes not sinter, but either resists sag and slumping of spans andoverhangs, and/or provides buoyancy for spans and overhangs. If thepowder bed is fluidized, the powder and part may be more uniformlyheated by the circulation of fluidizing with a gas. As shown in FIG. 24,a sintered body can be removed from the sintering oven. Some aluminapowder may remain in internal cavities and can be washed away STG-4Aand/or recovered.

With respect to sintering ovens, unlike solid metals (which may beopaque to or reflect microwaves at low temperatures), powdered metal mayadvantageously absorb microwaves. In addition, the resulting heatingprocess may be volumetric or partially volumetric, and heat a body ofpowdered material evenly throughout, including to sintering temperatures(if a compatible chamber and atmosphere can be practically provided).Furthermore, as discussed herein, smaller powder sizes (e.g., lower than10 micron, average or >90% count) may lower sintering temperatures toenable using lower temperature furnace and refractory materials. A soakin a forming or reducing gas (e.g., Hydrogen mixtures) may also be used.

A fused silica tube used for sintering (in combination with microwavesor otherwise) may be formed from very pure silica (e.g., 99.9% SiO2),and a crucible for holding the workpiece or part may be made from asimilar material. In some cases, the optical transparency of fusedsilica may correlate to its microwave transparency and/or itscoefficient of thermal expansion. A more optically transparent fusedsilica may have a lower degree of crystallization, and the crystalstructures may scatter both light and RF.

Typical Thermal Expansion Coefficients and Microwave Penetration Depths

Microwave power Thermal Expansion penetration Microwave fieldCoefficient depth* (for 2.45 penetration depth* Material ×10⁻⁶/° C. GHz)D, in cm (for 2.45 GHz) d, in cm Fused Silica 0.55 3900 7800 (amorphous,synthetic) Cordierite 0.1 Silicon Carbide 3.7 1 2 Mullite (can be 5.0500 1000 damaged by H2) Alumina 7.2 625 1250 Zirconia 10.5 QuartzMineral 7-14 (natural, crystalline) Bulk, solid aluminum (1.61 × 10⁻⁶micrometers)

-   -   Penetration depth (d) is the distance from the surface of the        material at which the field strength reduces to 1/e        (approximately 0.368) of its value at the surface. The        measurements in this table are taken at or around 20 degrees C.        As temperature increases, the penetration depth tends to        decrease (e.g., at 1200 degrees C., the penetration depth may be        50-75% of that at 20 degree C.).

With respect to gas handling, different sintering atmospheres areappropriate for different metals (e.g., Hydrogen, Nitrogen, Argon,Carbon Monoxide, vacuum, reducing gases with small percentages ofHydrogen), and for different stages of a sintering process. Thesintering atmosphere may help in different stages, e.g., in completingdebinding, in cleaning away debinding remnant materials to avoidcontamination in a sintering furnace, in reducing surface oxidation, inpreventing internal oxidation, and/or to prevent decarburization. Aatmosphere controlled furnace may be used before sintering as well, ordifferent stages arranged in a muffle staged continuous furnace.

An atmosphere after initial debinding to clean away lubricants orremnant binder, but before sintering may be oxidizing (nitrogensaturated with water or with added air) through water to hightemperature metal for example, optionally deposited with a similar(primary) matrix or binder component to the model material. Aftersintering, the release layer may become highly saturated, or by use ofair additions. Temperatures may be 200-750 C with dew point of 0 to 25C. An atmosphere in sintering, especially for stainless steels or sometool steels, may be highly reducing, e.g., pure Hydrogen, with dew pointof −20 to −40 C. Nitrogen/hydrogen mixtures (3-40%) or Nitrogen/ammoniamay be used, and hydrocarbons may add back surface carbon or prevent itsloss. Atmospheres in post-sintering may be cooling (at very low Oxygenlevels, e.g., 10-50 ppm) at a rate of, e.g., 1-2 degrees C. per second,and/or may be recarbonizing with a hydrocarbon-including atmosphere(forming some CO) at e.g., 700-1000° C. range for steels.

With respect to a microwave assisted sintering furnace 113, as shown inFIG. 25, one candidate microwave generator 113-1 for assisting orperforming sintering may generate 2.45 GHz frequency microwaves at apower output of 1-10 kW. The generator, oscillator or magnetron 113-1may be connected to a waveguide 113-2 with an open exit. A circulator113-3 and dummy load 113-4 (e.g., water) may absorb reflected waves toavoid returning these to the magnetron 113-1 and redirect travelingwaves to the furnace 113 (as monitored by appropriate sensors) andadjusted. A tuner device (in addition to or in alternative to thecirculator) 113-3 may change the phase and magnitude of microwavereflection to, e.g., cancel or counter reflected waves.

As shown in FIG. 25, one technique and material variation method mayinvolve supplying a material (pellet extruded, filament extruded, jettedor cured) containing a removable binder as discussed herein (two or onestage) and greater than 50% volume fraction of a powdered metal having amelting point greater than 1200 degrees C. (including various steels,such as stainless steels or tool steels). The powdered metal may havewhich more than 50 percent of powder particles of a diameter less than10 microns, and advantageously more than 90 percent of powder particlesof a diameter less than 8 microns. The average particle size may be 3-6microns diameter, and the substantial maximum (e.g., more than the spanof +/−3 standard deviations or 99.7 percent) of 6-10 microns diameter.The particle size distribution may be bimodal, with one mode atapproximately 8 micron diameter (e.g., 6-10) microns and a second modeat a sub-micron diameter (e.g., 0.5 microns). The smaller particles inthe second mode assist in early or lower temperature necking to preservestructural integrity.

Smaller, e.g., 90 percent of less than 8 microns, particle sizes maylower the sintering temperature as a result of various effects includingincreased surface area and surface contact among particles. In somecases, especially for stainless and tool steel, this may result in thesintering temperature being within the operating range of a fused tubefurnace using a tube of amorphous silica, e.g., below 1200 degrees C.Accordingly, in the process variation, as discussed herein, this smallerdiameter powder material may be additively deposited in successivelayers to form a green body as discussed herein, and the binder removedto form a brown body (in any example of deposition and/or debindingdiscussed herein).

As shown in FIGS. 24 and 25, the brown part may be loaded into the fusedtube furnace (furnace 113 is one example) having a fused tube 113-5formed from a material having an operating temperature less thansubstantially 1200 degrees C., a thermal expansion coefficient lowerthan 1×10⁻⁶/° C. and a microwave field penetration depth of 10 m orhigher (e.g., amorphous fused silica having an operating temperaturepractically limited to about 1200 degrees C., a thermal expansioncoefficient of about 0.55×10⁻⁶/° C. and a microwave field penetrationdepth of more than 20 m). The low thermal expansion coefficient relatesto the ability to resist thermal shock and therefore to ramp temperaturequickly and handle high thermal gradients in operation and in furnaceconstruction. For example, using a thermal shock resistant material maypermit ramping a temperature inside the fused tube at greater than 10degrees C. per minute but less than 40 degrees C. per minute. Themicrowave field penetration depth relates to microwavetransparency—higher penetration depths are related to highertransparency.

As shown in FIGS. 24 and 25, in this process the fused tube 113-5 may besealed by a fused silica plug or plate 113-6 (and/or a refractory orinsulating plug or plate). The internal air may be evacuated, and may befurther replacing internal air with a sintering atmosphere (includingvacuum, inert gas, reducing gas, mixtures of inert and reducing gas).Microwave energy may be applied from the microwave generator 113-1outside the sealed fused tube to the brown part. In this case, becausethe small particles may lower the sintering temperature, the brown partof steel may be sintered in this furnace at a temperature lower than1200 degrees C. In one advantageous example, more than 90 percent of theprinting material's powder particles have a diameter less than 8microns. Some of these particles, or particles in the remaining 10%, mayhave a diameter less than 1 micron (e.g., >90% of these having adiameter less than 0.5 microns).

As shown in FIGS. 24 and 25, because microwaves may be difficult todirect for evenly distributed heating (e.g., even with the use ofturntables and reflective stirring blades), the system may use susceptormembers 113-7 (e.g., rods distributed about the perimeter). Thesusceptor members 113-7 may be made from a microwave absorbing materialthat resists high temperatures, e.g., silicon carbide. The susceptormembers 113-7 may be passive (energized only by microwave radiation),active (resistively heated), or a mixture of the two. The susceptormembers 113-7 discussed herein may even be used without microwaveheating (in a microwave-free system, silicon carbide and MoSi₂, twocommon susceptor materials, are often also good resistive heaters forhigh temperatures). Further as shown in FIGS. 24 and 25, the microwaveenergy is applied from outside the sealed fused tube 113-5 to susceptormaterial members 113-7 arranged outside the sealed fused tube (whichdoes not contaminate the sintering atmosphere in the tube interior). Asnoted, the sintering atmosphere is appropriate for the powdered metalbeing sintered, e.g., inert, vacuum, or at least 3% Hydrogen (e.g., 1-5%hydrogen, but including up to pure hydrogen) for stainless steels.

In a variation approach for producing finely detailed parts, again thematerial having a removable binder and greater than 50% volume of apowdered steel (or other metal) is supplied with more than 50 percent ofthe powder particles have a diameter less than 10 microns,advantageously more than 90 percent having a diameter equal to or lessthan substantially 8 microns. The material may be additively depositedwith a nozzle having an internal diameter smaller than 300 microns,which provides fine detail but is 10-20 times the diameter of the largerparticles of the powder (preventing jamming). Again, the binder isremoved to form a brown body and the brown part loaded into the fusedtube, e.g., amorphous silica, having a thermal expansion coefficientlower than 1×10-6/° C., and the is sealed and the atmosphere thereinreplaced with a sintering atmosphere. Radiant energy (e.g., radiant heatfrom passive or active susceptor rods or other resistive elements,and/or microwave energy) is applied from outside the sealed fused tube113-5 to the brown part, sintering the brown part at a temperaturehigher than 500 degrees C. but less than 1200 degrees C. (a rangeenabling small particle aluminum as well as small particle steelpowders). In this case, the nozzle may be arranged to deposit materialat a layer height substantially ⅔ or more of the nozzle width (e.g.,more than substantially 200 microns for a 300 micron nozzle, or 100microns for a 150 micron nozzle).

In another variation suitable for sintering both aluminum and stainlesssteels (in addition to possible other materials) in one sinteringfurnace 113, parts formed from either small particle powder may beplaced in the same furnace and the atmosphere and temperature rampingcontrolled substantially according to the material. For example, a firstbrown part may be formed from a first debound material (e.g., aluminumpowder printing material) including a first powdered metal (e.g.,aluminum), in which more than 50 percent of powder particles of thefirst powdered metal have a diameter less than 10 microns, and a secondbrown part formed from a second debound material (e.g., stainless steelpowder printing material) including a second powdered metal (e.g.,stainless steel) in which more than 50 percent of powder particles ofthe second powdered metal have a diameter less than 10 microns. In afirst mode for the furnace, the aluminum brown part may be loaded intothe amorphous silica fused tube discussed herein, and the temperatureramped at greater than 10 degrees C. per minute but less than 40 Cdegrees C. per minute to a first sintering temperature higher than 500degrees C. and less than 700 degrees C. In a second mode, the stainlesssteel brown part may be loaded into the same fused tube, and thetemperature inside the fused tube ramped (e.g., by the heat control HCand or microwave generator MG) at greater than 10 degrees C. per minutebut less than 40 degrees C. per minute to a second sintering temperingtemperature higher than 1000 degrees C. but less than 1200 degrees C.

The atmosphere may be changed by the pressure control 113-8 and/or flowcontrol 113-9, operating the vacuum pump 113-10 or gas source 113-11. Inthe first mode for aluminum, a first sintering atmosphere may beintroduced into the fused tube 113-5, including inert Nitrogen being99.999% or higher free of Oxygen. In the second mode for stainlesssteel, a second sintering atmosphere comprising at least 3% Hydrogen maybe introduced.

As shown in FIG. 25, in the multipurpose sintering furnace suitable forrapidly sintering both aluminum and stainless steel at below 1200 C,using small diameter powders as discussed herein, the furnace mayinclude a fused tube 113-5 formed from a fused silica having a thermalexpansion coefficient lower than 1×10-6/° C. (a loose powder, permittinghigh ramp rates, the tube being resistant to thermal shock), and a sealthat seals the fused tube versus ambient atmosphere. A tube-internalatmosphere regulator (e.g., including the high vacuum 113-10 pump orother device, the pressure control 113-8, the flow control 113-9, and/orthe gas source(s) 113-11) maybe operatively connected to an interior ofthe fused tube 113-5 to apply vacuum to remove gases (including air andwater vapor) within the fused tube 113-5 and to introduce a plurality ofsintering atmospheres (including vacuum, inert, and reducing atmospheresin particular) into the fused tube. Heating elements (e.g., theresistive heater and/or susceptor 113-7 and/or the microwave generator113-1) are placed outside the fused tube 113-5 and outside any sinteringatmosphere within the fused tube 113-5 so as not to contaminate thesintering atmosphere. A controller (e.g., 113-12) may be operativelyconnected to the heating elements 113-7 and/or 113-1 and the internalatmosphere regulator. In a first mode, the controller 113-12 may sinterfirst material (aluminum) brown parts within a first sinteringatmosphere (<0.001 percent oxygen in nitrogen) at first sinteringtemperature higher than 500 degrees C. and less than 700 degrees C. In asecond mode, the controller may sinter second material (stainlesssteels) brown parts within a second sintering atmosphere (e.g., inert orreducing atmosphere) at a second sintering temperature higher than 1000degrees C. but less than 1200 degrees C. An (optical) pyrometer 113-13may be used to observe sintering behavior through the seal. The oven 113is held in an appropriate microwave reflective enclosure 113-14 and isinsulated with appropriate insulation 113-15 and refractory material113-16.

As shown in FIGS. 24 and 25, the internal atmosphere regulator may beoperatively connected to an interior of the fused tube 113-5 tointroduce the sintering atmospheres, and may ramp a temperature insidethe fused tube 113-5 at greater than 10 degrees C. per minute but lessthan 40 degrees C. per minute. This is typically not recommended withhigher thermal expansion ceramics like alumina or mullite. Also, themicrowave field penetration depth of 20 m or higher of amorphous silicapermits higher microwave penetration efficiency. The microwave generatorMG applies energy to, and raises the temperature of, the first and/orsecond material brown parts within the fused tube 113-5, and/or thesusceptors 133-7, which then re-radiate heat to heat the first and/orsecond material brown parts.

Accordingly, a small powder particle size (e.g., 90 percent of particlessmaller than 8 microns, optionally including or assisted by particles ofless than 1 micron) of metal powder embedded in additively depositedmaterial lowers a sintering temperature of stainless steels to below the1200 degree C. operating temperature ceiling of a fused silica tubefurnace, permitting the same silica fused tube furnace to be used forsintering both aluminum and stainless steel (with appropriateatmospheres), as well as the use of microwave heating, resistantheating, or passive or active susceptor heating to sinter bothmaterials.

As discussed herein, interconnected channels may be printed betweeninfill cells or honeycomb or open cells in the part interior, thatconnect to the part exterior, and a shell (including but not limited toa support shell) may have small open cell holes, large cells, or ahoneycomb interior throughout to lower weight, save material, andimprove penetration or diffusion of gases or liquids (e.g., fluids) fordebinding. These access channels, open cells, and other debindingacceleration structures may be printed in the part or supports(including shrinking/densification supports or shrinking/densificationplatform). All or some of the channels/holes may be sized to remain openduring debinding (including but not limited to under vacuum), yet closeduring the approximately 20% size reduction of sintering. Internalvolumes may be printed with a channel to the outside of the part topermit support material to be removed, cleaned away, or more readilyaccessed by heat transfer or fluids or gasses used as solvents orcatalysis.

Debinding times for debinding techniques involving solvent or catalystfluids (liquid, gas, or other) may be considered in some cases to dependon the part “thickness”. For example, a 4 cm thick or 2 cm thick partmay debind more slowly than a 1 cm thick part, and in some cases thisrelationship is heuristically defined by a debinding time of, e.g., somenumber of minutes per millimeter of thickness. The time for removingdebinding fluid (e.g., drying or cleaning) may also increasesubstantially proportionately with thickness. According to the presentembodiment, the effective thickness of a part for the purposes ofdebinding time may be reduced by providing the aforementioned fluidaccess to an interior of the part, using channels from the exteriorwhich may either remain open through sintering or be (effectively)closed following sintering.

Such channels may include at least one access channel to an exterior ofthe part, e.g., penetrating from the exterior of the part through wallstructures of the 3D printed shape to one, several, or many infillcavities of the part; or may alternatively be surrounded by wallstructures of the part. In some cases, an interconnected channel mayinclude at least two access channels to an exterior of the part thatsimilarly penetrate a wall, in order to provide an inlet and an outletfor fluid flow or simply to permit fluid to enter versus surface tensionand/or internal gas. These inlet-honeycomb-outlet structures may bemultiplied or interconnected. In some cases, the inlets may be connectedto pressurized fluid flow (e.g., via either 3D printed or mechanicallyinserted flow channel structures). In some cases, the inlets may beconnected to vacuum or a flushing gas. In some cases, “inlet” and“outlet” are interchangeable, depending on the stage of the process.

For example, the 3D printer according to FIGS. 1-40 inclusive may beemployed to feed the composite material including the binder matrix anda sinterable powder. “Walls” in a layer or shell follow positivecontours or negative contours of a 3D model and are positioned accordingto the mesh or model outline or surface, and may be one or more roads orlayers or shells thick (adjacent walls formed by offsetting from themodel outline or surface). Internal walls (including horizontal walls as“roofs” or “floors”) may also be formed, typically connecting to orextending from walls that follow the outer or inner contour of the 3Dmodel shape. “Infill” or honeycomb extends between and among walls,floors, and roofs. The 3D printer may deposit a wall or successivelayers of a wall, the wall having an access channel extending from anexterior of the part to an interior of the part. The access channelpermits fluid to enter the interior (e.g., between positive and negativecontours of a cross-section of the part). As shown, e.g., in FIGS.26A-31, it is not necessary that the entirety of the interior of a partbe interconnected to reduce the debinding time. For example, awall-penetrating access channel and interconnected honeycomb (e.g., viaa distribution channel) may be connected to route fluid to a locationwithin a specified distance of the deepest interior region of a part; orto set a specified distance of a wall or walls of the part to a nearestfluid-filled chamber.

The 3D printer may deposit successive layers of honeycomb infill withinthe interior (e.g., between walls tracing positive and negative contoursof the part), and the honeycomb infill may have a distribution channel(or several, or many distribution channels) connecting an interiorvolume of the honeycomb infill to the access channel. The 3D printer orsubsequent debinding station or part washer may debind the binder matrixby flowing a debinding fluid through the access channel and/ordistribution channel(s) and within the interior volume of the honeycombinfill.

FIG. 26A and FIG. 26B substantially correspond to FIGS. 5B and 5D,respectively, and show selected sections through FIG. 4 for the purposeof discussing printing and other process steps. As shown in FIGS. 4 and26A, following the printing of the raft separation layer SL1, a raft RA1of model material (e.g., metal-bearing composite) is printed. The raftor shrinking platform or densification linking platform RA1 may includerouting channels CH1 therethrough for connecting to or directing fluidto access channels of the part. There may be one, several, or as shown,an array of routing channels CH1. The routing channels CH1 may connectduring debinding to a matching one, several or array of debinding fluidsupply channels (e.g., as shown in FIG. 25). Alternatively, or inaddition, fluid flow through the routing channels may be promoted viacirculation, heating, or agitation in an immersed bath of debindingfluid. Agitation may be forced fluid, mechanical, inductive, magnetic,or the like. The raft or shrinking platform RA1 is otherwise similar tothat discussed with reference to FIG. 5B.

As shown in FIGS. 4 and 26B, the surrounding shell support structure SH1is continued printing in layers, and the internal volume V1 as well asthe part interior may be printed with a channel (e.g., distributionchannels CH3 leading to access channels CH2, not shown) to the outsideof the part to permit support material to be removed, cleaned away, ormore readily accessed by heat transfer or fluids or gasses used assolvents or catalysis. In the case of FIGS. 4, 26A, and 26B (and otherFigures as well), as noted, solid bodies are shown to simplifyexplanation, but the internal structure of the solid bodies may be 3Dprinted with infill patterns (e.g., honeycombs) and/or may includechopped, short, long, or continuous fiber reinforcement. Two examplesare shown in FIG. 26C and FIG. 26D.

As shown in FIG. 26C and FIG. 26D, respectively, hexagonal andtriangular honeycombs (which, shown in cross section, may include bothcavities and infill formed in a vertical prism, columnar, or may beoffset polyhedral cavities/infill) is employed as infill. Twodistribution channels CH3 are shown in each sectioned layer. Thedistribution channels CH3 may be distributed about many layers (e.g.,may be formed among a few layers) to interconnect some, many, or allinfill or honeycomb cells. FIG. 26C also shows an access channel CH2,which may interconnect with the distribution channels CH3 by channel andcell cavity paths spanning different layers of the deposition. Thechannels CH2 and CH3 are angled through infill and walls of the part,which can increase the length of a channel and/or decrease the number ordegree of turns in the fluid flow. In this manner—by changing the lengthor straightness of channels CH2 or CH3—fluid flow throughout thechannels CH2 and CH3 part can be balanced for evenness orincrease/decreased flow in a particular region.

FIG. 27 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8 and 9, in which the honeycombcavities/infill are formed as vertical, columnar prism shapes.Distribution channels CH3 (e.g., approximately 20 shown) are shown amongthe many layers of the deposited part. The distribution channels CH3 areshown distributed about many layers to interconnect some, many, or allinfill or honeycomb cells. No channels extend into overhangs OH2 or OH4,which may not be thick enough to need additional debinder fluid flow. Asshown, sintering support or form-fitting shell SH3 may also be filledwith infill cells, and may or may not additionally include channels,access or distribution channels CH2 or CH3 (none shown in FIG. 27). FIG.27 does not show the optional access channel CH2, in the case where thedistribution channels CH3 by themselves increase debinding speed. In onevariation, 20% or fewer of the vertical honeycomb cavities of theinfill, or vertical column cavities having an area of less than 5% ofthe area of a largest cross section, act as distribution channels.

FIGS. 27 and 28 show a side sectional view, substantially similar indescription to FIGS. 4, 6, 8 and 9 (common reference numbers beingsimilarly described), in which the honeycomb cavities/infill are formedas vertical, columnar prism shapes. Distribution channels CH3 (e.g.,approximately 20 shown) are shown among the many layers of the depositedpart. The distribution channels CH3 are shown distributed about manylayers to interconnect some, many, or all infill or honeycomb cells. Nochannels are shown extending into overhangs OH2 or OH4, which may not bethick enough to need additional debinder fluid flow. As shown, sinteringsupport or form-fitting shell SH3 may also be filled with infill cells,and may or may not additionally include channels access or distributionchannels CH2 or CH3 (none shown in FIG. 27). FIG. 27 does not show theoptional access channel CH2, i.e., showing the case where thedistribution channels CH3 by themselves increase debinding speed.However, the access channels CH2 shown in other Figures and describedherein may be applied to the structure of FIG. 27. FIG. 28 shows accesschannels CH2 which provide ingress and egress for fluid flow into thedistribution channel CH3 interconnected honeycomb cells. As should benoted throughout, dimensions for channels may be exaggerated, and breaksin walls as shown merely through holes—the distribution channels CH3 maybe small circular holes, and take up less than 1% (e.g., less than 1-3%)of the surface area of the infill, and similarly, the access channelsCH2 may be small circular through holes which take up less than 1%(e.g., less than 1-3%) of the surface area of the part walls.

FIG. 29 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, and 28 (common reference numbersbeing similarly described) in which the distribution channelscavities/infill are formed in an aligned, and/or angled, mannerthroughout the columnar prism shapes. As discussed, changing thediameter, length and/or straightness of the channels CH3, or depositingobstacles or baffles within them, may increase or decrease resistance toflow. In contrast to FIG. 28, the sintering support or shell structuresSH3 and SH4 also include access channels CH2 to permit fluid flowtherethrough (both an inlet and outlet). Further, routing channels CH1are printed in intervening layers (e.g., raft RA2, shell structures SH3,SH4, release or separation layers SL3), and in this case may match amatching routing channel provided in the print bed or build plate (e.g.,to provide fluid flow access in those cases where a print bed or buildplate may be transported together with the green and/or brown partthroughout the debinding and/or sintering process).

FIG. 30 shows a side sectional view, substantially similar indescription to FIGS. 4, 6, 8, 9, 27, 28 and 29 (common reference numbersbeing similarly described) in which the distribution channels CH3throughout cavities/infill are formed in an aligned, and/or angled,manner throughout cellular (octahedral as one example) polyhedronstacked shapes, and in which access channels CH2 are provided in threelocations in this section. It should be noted that wall thicknesses maybe maintained substantially constant (e.g., within 5% of thickness)throughout—e.g., the exterior wall or shell thickness of the part beingthe same as the interior walls of the infill, and/or either being thesame as walls forming distribution or access channels, and/or any ofthese being the same thickness as walls forming the sintering supportstructures or shrinking platform.

FIG. 31 shows a side sectional view, a closer view of the exemplary partof the process diagram of FIG. 25, substantially similar in descriptionto FIGS. 4, 6, 8, 9, 27, 28 29, and 30 (common reference numbers beingsimilarly described), in which the distribution channels CH3 throughoutcavities/infill are formed in an aligned, and/or angled, mannerthroughout cellular prism shapes, and in which access channels CH2 areprovided in two locations in this section. The distribution channelspass near to, adjacent to, or proximate to the portion of the partinterior farthest from, deepest within, or thickest TH with reference toa negative or positive contour or wall of the part. As discussed withreference to FIG. 25, the uppermost region of the part shown in FIG. 31does not include channels, as the part interior is close enough todebinder fluid flow such that it may be expected that the uppermostregion of the part may debind in an acceptable time.

Accordingly, as shown in FIGS. 25-31, the process of forming a “thick”part amenable to rapid fluid-based debinding may include depositingsuccessive layers of the wall of the part to form not just one accesschannel CH2, but also a second access channel CH2 extending from theexterior of the part to the interior of the part. This may assist indebinding the binder matrix by flowing a debinding fluid in through thefirst access channel, via the distribution channel, and out through thesecond access channel. In this case, the first access channel CH2 may beconnected to a pressurized supply of debinding fluid to force debindingfluid through and/or throughout the first access channel, distributionchannel(s), and second access channel. Additionally, or in thealternative, in this process, successive layers of honeycomb infill maybe deposited in the interior of the part to form a plurality ofdistribution channels CH3 connecting an interior volume of the honeycombinfill to the first access channel CH2, at least some of the pluralityof distribution channels CH3 being of different length from other of thedistribution channels CH3.

As shown in FIGS. 32 and 33A-33D, companion ceramic sintering supportsmay be printed using a ceramic composite material that behavesdimensionally similarly to the metal model material but does not sintertogether with it. As a part and its companion ceramic sintering supportsCSS may sinter according to any particular temperature profile suitablefor sintering the part's model material, the material of the ceramicsintering support shrinks by a particular amount and in some cases alonga particular density profile (e.g., starting and ending density,starting and ending temperatures, shape of the curve between) accordingto at least the composition of the ceramic sintering support material.To match the sintering behavior of the ceramic sintering supports tothat of the part model material, as noted, the amount of final shrinkageshould be the same. As shown in FIG. 32, optionally, the amount ofshrinkage of the ceramic sintering support material should be less thanthat of the part model material until the final shrinkage amount isreached. Further optionally, the ceramic sintering support material maybegin to shrink at a lower temperature or earlier at the sametemperature.

In general, the substantial temperature ramp and environmentalconditions (such as gases) for sintering a target metal part modelmaterial is presumed to be the temperature ramp to be used, because thepart must sinter adequately with or without supports. Exceptions arepossible (e.g., minor changes to the part model sintering temperatureramp to allow the supports to function better). Under these conditions(e.g., given a temperature ramp suitable for sintering a metal partmodel material), a candidate first ceramic material, e.g., α-alumina orother alumina, having a sintering temperature above that of the partmodel material may have its sintering temperature lowered and/or itsshrinkage amount changed by (i) reducing average particle size (“APS”)or (ii) mixing in a compatible second or third lower temperaturesintering material (e.g., silica, or yttria-silica-zirconia). Thesemixed materials would also be sintered. In addition, or in thealternative, a non-sintering filler that sinters at a significantlyhigher temperature may be mixed (which will generally decrease theamount of shrinking or densification). In general, homogeneous materialshaving a smaller APS will start densifying at lower temperatures andwill attain a full density at a lower temperature than the larger APSmaterials.

In addition, or in the alternative, the sintering temperature, shrinkingamount or the degree of densification can be changed by changing theparticle size distribution (“PSD”, e.g., for the same average particlesize, a different proportion or composition of larger and smallerparticles). In addition, or in the alternative, when materials that mayreact are mixed, the sintering temperature, shrinking amount or thedegree of densification of the mixture can be changed by using componentmixing that may densify at a lower temperature than a chemical reaction,e.g., combining alumina and silica in a manner that densifies (sinters)at a temperature lower than that which forms mullite. For example,alumina-silica powder may be generated as alumina powder particles eachforming an alumina core with a shell of silica, where the mixture firstdensifies/sinters between, e.g., 1150 and 1300 deg C., and converts tomullite only at higher temperatures, e.g., 1300-1600 degrees C.

In addition, or in the alternative, the sintering temperature, shrinkingamount or the degree of densification can be changed by changing adegree of homogenization (molecular, nano-scale, core-shell structures)of dissimilar components. In the case of part shapes including either orboth of convex or concave shapes (protrusions, cavities, or contours),as shown in FIGS. 33A-33D, a sintering support made of a material havinga different shrinkage rate or shrinkage amount can cause either or bothof slumping or interference that can could cause the shape to deform. Itshould be noted that FIGS. 33A-33D are exaggerated in scale.

An appropriate sintering support material may have a final shrinkageamount over the same time-temperature sintering profile as the modelmaterial, as discussed herein. However, perfect matching of rate andfinal shrinkage percentage is not necessary. For example, the sinteringsupport material should not shrink at a slower rate than the modelmaterial, or concave shapes on the part may be deformed and may not berestored by gravity. However, should the sintering support materialshrink at a faster rate than the model material, printed sinteringsupports may not interfere with many concave shapes of the part (e.g.,as shown in FIG. 33B). In addition, for a faster shrinking sinteringsupport, the printed supports may be split, and gaps printed intosintering supports, to avoid interfering with and/or deforming eitherconvex shapes or certain concave shapes. In this case, gravity and someelastic behavior at sintering temperatures, —even if the sinteringsupport material shrinks at a faster rate than the model material—willpermit the part and the sintering supports to “match up” at the finalsintering shrinkage amount.

As shown in FIGS. 33C and 33D gaps may be printed side-to-side, in thevertical direction or horizontal direction, together with green bodysupports and/or a separation layer between each ceramic sinteringsupport and the part (including between adjacent ceramic sinteringsupports). Gaps may be printed adjacent convex or concave part shapes orcontours. In addition, gaps may be printed adjacent convex or concavepart shapes or contours where a surface of the part and a surface of aceramic support follow respective paths that would, without the gap,interfere during shrinking. In the case of vertical gaps, a small amount(e.g., a few mm) of unsupported span of part material is stiff enough toresists gravity-caused slump during sintering. In the case of horizontalor diagonal gaps, a separation layer in the gap including remnant powder(spheres) following debinding will permit substantially free horizontalor diagonal sliding of the ceramic support during sintering.

However, as shown in FIGS. 33A-33D, even when the ceramic sinteringsupports shrink/sinter earlier than and/or faster than and/or equal tothe metal part material until the target density, substantiallydiffering shrink rates or other differences in bulk density curve overtime (e.g. differing starting or ending positions, differing curveshapes) may require some rearranging of some sintering supportsfollowing debinding, such that the shrink rate profile of the modelmaterial to the sintering support material be matched to within 5percent of the bulk density of the model material over rising andconstant temperature portions of a sintering temperature ramp.

FIGS. 34A and 34B show a flowchart and schematic, respectively, thatshow a gravity-aided debinding process useful with parts as describedherein printed with channels CH1, CH2, and/or CH3 (or even in some caseswithout). FIGS. 34A and 34B are described and shown using thecross-sectional structure of FIG. 29 (having such channels) as anexample. As shown in FIGS. 34A and 34B, access, routing, anddistribution channels permit fluid to enter the part interior to morequickly debind the green part to a brown part. Debinding as a solventbased (including with thermal assistance, or thermal debinding withsolvent assistance) or catalytic process may take hours, sufficient timeto permit fill-purge fluid cycles. In one exemplary process, as shown inFIGS. 34A and 34B, a part with access, distribution, and/or routingchannels is placed in a debinding chamber, container or facility in stepS341. As shown in FIG. 34B, the part may be suspended or put on a porousrack or otherwise held in a manner that leaves at least top and bottomchannel inlets and outlets relatively clear of obstructions to gravitybased fluid flow.

In Step S342, the chamber may be filled with solvent or other debindingagent (alternatively, or in addition, the part is lowered or otherwiseplaced into a pre-filled bath). In Step S343 the part is kept in thedebinding agent for a predetermined, modeled, calculated, or measureddwell time. The dwell time may be sufficient for, e.g., the debindingagent to permeate the channels. The dwell time may be additionally oralternatively sufficient for, e.g., the debinding agent to debind thefirst matrix material by a first effective amount (e.g., 5-30% or higherby volume of matrix material removal). The dwell time or period in StepS343 may be enhanced by, as shown in FIG. 34B, by agitation (e.g.,mechanical members, entire chamber, bubbles, etc.), vibration and/orcirculation. In optional step S344, a property or characteristicrepresentative of the state of debinding may be detected and/ormeasured, and optionally used as a trigger to start a draining processto purge or drain debinding agent and removed material in preparationfor a next cycle (there may be only one cycle in some cases ofmeasurement). Exemplary measurements would be (i) via an optical orelectromagnetic sensor, measuring a property such as opacity, color,capacitance, inductance representative of an amount of material debound(ii) via a mechanical or fluid-responsive sensor (optionally connectedto an optical or electromagnetic element), measuring a property such asnatural frequency, viscosity, or density or (iii) via a chemical sensor(optionally connected to an optical or electromagnetic element)measuring a chemical change such as pH, oxygen content, or the like.

In step S345, and as shown in FIG. 34B, the debinding chamber may bedrained via gravity into a reservoir. Given sufficient time, andoptionally aided by agitation, heating, circulation, or otherthermomechanical processes, internal debinding agent fluid-filedchannels (such as distribution and access channels) within the part alsodrain. The reservoir may include a filter, baffles, or other cleaner forremoving debound material, and/or catalytic, chemical, magnetic,electrical or thermomechanical agent(s) for precipitating or otherwisegathering or removing debound material from the debinding agent.Alternatively, or in addition, the reservoir may include a valve foreffecting the drain from the debinding chamber, and/or a pump forrecirculating debinding agent back into the debinding chamber.Alternatively, or in addition, the reservoir may be integrated in thedebinding chamber (e.g., recirculated in the debinding chamber aftermaterial removal).

In step S346, and as shown in FIG. 34B, post draining or partialdraining, a measurement may be taken to gauge to progress of debindingand set a subsequent stage trigger or instruction for the next cycle.The sensor applicable may be similar or the same as that described withreference to step S344. In addition, or in the alternative, the partweight may be measured (before and after a debinding cycle) via a loadcell, etc. In a case where the number of cycles of filling and drainingthe chamber is relatively low (e.g., 2-10 cycles), the changing partweight may be recorded (e.g., as a profile) and used to determine thetime, temperature, and/or agitation of a subsequent cycle. In a casewhere the cycle count is 2-10 or higher (e.g., including continuousrecycling and/or fill/drain), the profile of weight change may also beemployed to model an exponential decay constant relating to the maximumremovable binder per part weight and set a termination cycle count ortime based on the exponential decay constant (e.g., terminating at atime or cycle count for 90-95% removed material by weight based on theexponential decay rate).

In step S347, and as shown in FIG. 34B, cycles may repeats untilcomplete (“N CYCLES” being determined by predetermined count or time, bydirect or indirect measured feedback as described above, or othermodeling). When the cycles of debinding via gravity-based fill/draincycles are complete, the green part has become a brown part, and may beactively or passively dried or otherwise post-processed in preparationfor sintering. As shown in FIG. 35, and noted herein, the green partsmay be formed from a curable and/or debindable photopolymer including asinterable powder, as well as optionally a second stage binder (either adebindable, e.g., pyrolysing photopolymer or thermoplastic). As noted inthe CFF patent applications and other prior patent applicationsincorporated herein, different additive manufacturing processes caninclude a matrix in liquid (e.g., SLA) or powder (e.g., SLS) form tomanufacture a composite material including a matrix (e.g., debindableplastic) solidified around the core materials (e.g., metal powder). Manymethods described herein can also be applied to Selective LaserSintering which is analogous to stereolithography but uses a powderedresin for the construction medium as the matrix as compared to a liquidresin. The reinforcement might be used for structural, electricalconductivity, optical conductivity, and/or fluidic conductivityproperties. As described in the CFF patent applications and other priorpatent applications incorporated herein, and as shown in FIG. 35, astereolithography process is used to form a three dimensional part, thelayer to be printed being covered with resin, cured with UV light or alaser of a specified wavelength, the light used to cure the resinsweeping over the surface of the part to selectively harden the resin(matrix) and bond it to the previous underlying layer.

FIG. 35 depicts an embodiment of the stereolithography process describedabove. Description of FIGS. 1A and 1B herein would be recognized by oneof skill in the art as consistent with FIG. 35 (despite differences inreference numbers). As depicted in the figure, a part 1600 is beingbuilt on a platen 1602 using stereolithography. The part 1600 isimmersed in a liquid resin material 1604 contained in a tray 1606. Theliquid resin material may be any appropriate photopolymer (e.g.,debindable composite including a primary debindable component andoptionally a secondary debindable component and a sinterable powder). Inaddition to the resin bath, during formation of the part 1600, theplaten 1602 is moved to sequentially lower positions corresponding tothe thickness of a layer after the formation of each layer to keep thepart 1600 submerged in the liquid resin material 1604. In the depictedembodiment, a laser 1612, or other appropriate type of electromagneticradiation, is directed to cure the resin. The laser may be generated bya source 1616 and is directed by a controllable mirror 1618.

Extrusion type and other deposition 3D printers employ various printingapproaches for completing perimeters, in particular for reducing seamsresulting from extruding a closed perimeter path. Any path point not ona perimeter path is in an interior region, because the perimeter pathconstitutes the outermost path points (e.g., a new path that forms partof the outer perimeter renders previous paths to be interior regions).Accordingly, printing paths may form a seam with a butt joint or otherthan a butt joint (or example, overlapping, self-crossing,interlocking). Generally, one segment and one seam is preferred becausefewer seams tend to have superior aesthetics, sealing, and dimensionalstability. Further, wall or shell contour paths (in contrast to “raster”fill paths) have been deposited in a same rotational direction—eitherclockwise or counterclockwise. Paths are printed in the same clockwiseor counterclockwise direction even if a perimeter path branches to theinterior. This simplifies and speeds printing as perimeter paths can becontinuously printed without reflex angle turns (e.g., turns of lessthan 180 degrees) from the current heading.

In the case where a printer deposits a composite feedstock intended tobe debound then sintered, and a second stage binder in place duringsintering includes retaining polymers of a common molecular lengths,deposition may create stress along the polymer molecule chains (e.g.,HDPE etc.) within at least the second stage binder aligned to someextent along the deposition paths. In the green or brown state, thestresses may not have any particular effect on dimensional stability.However, as the part is heated in the sintering process, the stressesmay relax or pull in each layer, cumulatively changing the shape of thepart if many small changes add up in the many layers of the part.

In such a case, brown parts may be dimensionally consistent with thedeposited green part, but may display a twist around a vertical axisafter sintering. In a case where heating a brown part to mild levels(e.g., 150-200 C) causes twist, the second stage polymer binder may beconsidered to be heated to a level where residual stress can relax,causing the twist, as deposition stress built into the brown part isrelaxed. As the printer deposits a layer, long chain molecules thatcompose the second stage binder polymer (the part of the binder that isleft after the primary debind) may be strained along the printingdirection. When heated to a relaxing temperature, the molecules may pullback, potentially causing a macroscopic twist in the part as pulls amongmany layers accumulate.

One countermeasure for twist is to print roads in a counteracting orretrograde direction. The three most common categories of roads areshells or walls, which are printed to form the perimeter of a slicedinterior or exterior contour; “raster” fill, which is printed to fillinterior volume in a solid manner, and infill honeycomb, which isprinted to fill interior volume in a honeycomb. In addition, interiorvolume may be filled in any coverage pattern including non-raster ornon-boustrophedon fills that cross road and/or are parallel or adjacentother roads or contours (e.g., random fill, wall-following fill, spiralfill, Zamboni-pattern fill, or the like), and may be filled in variablesize, randomized, anisotropic, foam-like, sponge-like, 3-dimensional, orother versions of regular and irregular cellular (cell walls and lowdensity or atmosphere cell interior) fills. For shells or walls, many ormost parts are not formed from vertical prism shapes and through-holes,so layer to layer the shape of a slice and the shape of the shell or allincrementally changes for different wall slopes, concavities andconvexities. Close to upper and lower surfaces, the incremental changein wall or shell shape may be more significant.

At a topmost horizontal or substantially horizontal flat layer with,e.g., protrusions or another shape beginning in the layer above, theshape of shells or walls may change completely from one layer to thenext. Accordingly, it is optionally advantageous to print first andsecond sets of opposing direction walls or shells within one layer, soas to avoid layer-to layer comparison which may be more complex. Oneapproach is to print each outer perimeter or negative contour innerperimeter with a companion, parallel, adjacent wall or shell road. Insuch a case, the length of the companion or offsetting road is notnecessarily precisely the same, especially for small positive andnegative contours (e.g., for a 3 mm diameter feature, the length of theperimeter road vs. a companion road may differ by 25 or 30%, while at 30mm the length of the companion road may be 5% or less difference). Insuch a case an amount of overlap determined according to the differencein perimeter lengths may be effective at removing twist.

For raster fill within the shells or walls, a twisting effect from therelaxation of residual stress may not be as pronounced because rasterrows may include some retrograde paths. However, as the filled interiorarea becomes smaller, differences in path length among raster rows andturns may be more pronounced. Overlap determined according to adifference in directional lengths (e.g., including straight rows as wellas end-of-row turns) may be used to offset a length difference. Inaddition, raster-like or cellular patterns may be printed in tilepatterns that each include main paths and parallel retrograde paths torelieve twisting stress relaxation within the tile and/or among tiles.

In one example of such an embodiment or expression of the invention, asshown in FIG. 36A, where deposition direction is shown with an arrowwithin a deposition path, a method for building a part with adeposition-based additive manufacturing system, may include depositing,in a first direction (as indicated by an internal arrow), apolymer-including material along a first contour tool path to form aperimeter path 371 of a layer of a green part and to define an interiorregion within the perimeter path. The material is also deposited in asecond direction retrograde the first direction on a second contour toolpath to form an adjacent path 372 in the interior region adjacent theperimeter path 371. The deposition of the adjacent path 372 in thesecond direction stresses polymer chains in the material in a directionopposite to stresses in polymer chains in the material in the perimeterpath 371, and reduces part twist caused by relaxation of the polymerchains in the part.

FIG. 36B may be considered a different version of the layer of FIG. 36A,or may be considered to depict an adjacent layer (FIG. 36B is depicted asmaller outer perimeter than FIG. 36A, such as would be the case for anadjacent layer sloping to a peak). As shown, an adjacent perimeter path376 in an adjacent layer may be alternatively or also deposited in aretrograde direction with respect to the perimeter path 371, and otherpaths such as raster fill 378 or honeycomb infill 377 may also beprinted in a retrograde direction with respect to parallel paths in anadjacent layer 374, 373 respectively. Also as shown in FIG. 36B, anadjacent road or deposition 376 may be deposited wider or at a higherrate than a perimeter path 375 (or narrower). When an odd number ofwalls is deposited at a perimeter, the changed width or deposition ratemay offset the twist tendency of two adjacent depositions (on eitherside) in the same layer.

While a butt joint as shown in FIG. 37B or 37J is one of the simplestseams (e.g., butt joints in adjacent roads or depositions may bealigned, rotationally offset, or in distant rotational positions), oneof a start of deposition or a stop of deposition to be located withinthe interior region of the layer as shown in FIG. 37A, or 37C through37H. As shown in FIGS. 37A through 37H, the locations of the start pointand the stop point may be configured to define various joints, overlapsand interlocks. As shown in FIGS. 37H and 37J, a contour tool pathbetween a path's start point and the stop point may defines a rasterpath that at least partially fills the interior region.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in building a part with adeposition-based additive manufacturing system having a deposition headand a controller 20, a first tool path for a layer of the part may bereceived by the controller, the received first tool path including aperimeter contour segment 371. A second tool path 372 may be receive fora layer of the part by the controller, including an interior regionsegment adjacent the perimeter contour segment. The deposition head maybe moved (including directed movement of a beam or ray of light orelectromagnetic energy) in a pattern that follows the perimeter contoursegment of the received first tool path to produce a perimeter path 371of a debindable composite including sinterable powder, and in a patternthat follows the interior region segment of the received second toolpath to produce an interior adjacent path 372 of the debindablecomposite, wherein the perimeter path 371 and the adjacent path 372 aredeposited in retrograde directions so that directions of residual stresswithin a binder of the debindable composite are opposite in theperimeter path and the adjacent path. As shown in FIGS. 37A-37H and 37J,this may also apply between adjacent layers, where the adjacent path 376is in an adjacent layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in building a part with adeposition-based additive manufacturing system, a digital solid modelmay be received for the part (e.g., a 3D mesh such as an STL file or a3D solid such as a NURBS, parasolid, IGES file). The digital solid modelmay be sliced (by, e.g., a computer or a cloud-based computing service)into a plurality of layers. A perimeter contour tool path 371 may begenerated based upon a perimeter of a layer of the plurality of layers,wherein the generated perimeter contour tool path defines an interiorregion of the layer. An interior adjacent path 372 may be generatedbased on the perimeter contour tool path within the interior region. Adebindable composite may be deposited including sinterable powder in afirst direction based on the perimeter contour tool path to form aperimeter 371 of the debindable composite for the layer. The debindablecomposite may be extruded in a second direction based on the perimetercontour tool path to form an interior adjacent path 372 of thedebindable composite for the layer. The deposition of the perimetercontour tool path 371 and the interior adjacent path 372 may be tracedin retrograde directions to one another so that directions of residualstress within a binder of the debindable composite are opposite in theperimeter contour tool path 371 and the interior adjacent path 372.Optionally, as shown in FIGS. 37A and 37C-37H, a start point of theperimeter contour tool path 371 and a stop point of the perimetercontour tool path 371 may be adjusted to locations within the interiorregion.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, building a part with andeposition-based additive manufacturing system having a deposition headand a controller may include receiving a first tool path for a layer ofthe part by the controller, wherein the received first tool pathcomprises a contour segment. A second tool path may be received for alayer of the part by the controller, and wherein the received secondtool path overlaps the first tool path over more than 70 percent,preferably at least 90 percent of a continuous deposition length of thesecond tool path. The deposition head may be moved in a pattern thatfollows the first tool path to produce a perimeter path 371 of adebindable composite for the layer, and also moved in a pattern thatfollows the second tool path in a retrograde direction to the first toolpath to produce a stress-offsetting path 372 adjacent the perimeter pathof debindable composite. Directions of residual stress within a binderof the debindable composite may be opposite in the perimeter path 371and the stress-offsetting path 372.

Optionally, the second tool path may be continuously adjacent or overlapthe first tool path within the same layer, and may include interiorregion path within the same layer. Alternatively, or in addition, thesecond tool path is continuously adjacent over at least 90 percent ofthe first tool path within an adjacent layer, and may include aperimeter path of the adjacent layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, in a method for building apart with a deposition-based additive manufacturing system having andeposition head and a controller, the method includes generating a toolpath with a computer. Instructions may be generated for the generatedtool path to the controller. A debindable composite may be depositedfrom the deposition head while moving the deposition head along thegenerated tool path to form a perimeter path of a layer of the part. Asshown in FIG. 37G, the perimeter path may include a first contour roadportion 378, and a second contour road portion 379, each of the firstcontour road portion and the second contour road portion crossing oneanother with an even number of X-patterns, forming an even number ofconcealed seams for the layer.

In another example of such an embodiment or expression of the invention,as shown in FIGS. 36A-36B, 37A-37H, and 37J, a deposition-based additivemanufacturing system having a deposition head and a controller may movethe deposition head along a first tool path segment 380 to form aperimeter road portion 371 for a layer of the part. As shown in FIG.37C, the deposition head may be moved along a direction changing toolpath segment 381; and moved along a second tool path segment 382 to forma stress-balancing road portion 372 adjacent to the perimeter roadportion 371. As shown in FIG. 37C, the direction changing tool pathsegment 381 may include a reflex angle continuation (e.g., between 180and 360 degrees) between the first tool path segment 380 and the secondtool path segment 382 within the same layer.

As shown in FIGS. 38A, 38B, 39A, 39B, and 40 nozzle structure can beused to improve printing properties of the metal powder compositefeedstocks discussed herein. Metal powder composite feedstocks such asMIM (Metal Injection Molding) feedstocks, are a composite material, asdiscussed herein, including sinterable metal powder and a binder, may bedesigned to facilitate MIM-specific processes. As discovered by variousauthors in the last twenty years, certain feedstocks can be adapted forextrusion-type 3D printing, e.g., Fused Deposition Modeling or FusedFilament Fabrication (“FDM” or “FFF”, terms for generic extrusion-type3D printing). Traditional extrusion feedstocks are not formed in thesame manner as MIM feedstocks, and include thermoplastic material thatmelts or softens. In the case of MIM feedstocks, other materialsintended for injection molding or the green-to-brown part process areoften included in the feedstock—typically waxes, but including other lowmelting point and low viscosity materials. The higher viscosity (vs.lower viscosity of wax-including MIM feedstocks) and lower thermalconductivity (vs. high metal powder content of MIM feedstocks) ofFDM/FFF thermoplastic filament may require a larger melt zone to get thematerial to a suitable temperature and thus suitable viscosity to flow.

If the melting point is low enough, or the material reactive enough,small bubbles or other discontinuities can form in the fluidizedfeedstock during the extrusion process when using ordinaryextrusion-type nozzles, heat breaks, and heating. The bubbles createprinting problems in several ways—for example, uneven printing in bothgaps and drips, or uneven printing of adjacent roads or roads indifferent parts of the layer or part. The present disclosure provides asolution specifically for promoting even printing. Bubbles may be formedin many ways—for example gas dissolution from the solid phase, i.e.small amounts of moisture making steam. Alternatively, or in addition,micro bubbles may coalesce in the nozzle that entered the feedstockfilament in a feedstock manufacturing phase—e.g., bubbles in pelletmaterial converted into filament that are not removed during thisprocess, or bubbles introduced during filament production.Alternatively, or in addition, air may be pulled into the system duringa retract step following steady printing (an extrusion type 3D printermay be set to “retract”, i.e., reverse the filament drive direction, bya small amount—e.g., 1-5 mm—following steady printing or during anon-printing nozzle translation to relieve pressure in the melt zone).In addition, or in the alternative, bubbles may be caused by deformationdue to the filament extruder hob (e.g., caused by any of grabbing teeth,pressure, or heating)

An additional benefit of the present system is decreasing the volume ofmelt for a practically sized heater block and nozzle system, providingmore responsive extrusion control. Additional back pressure may alsogive better extrusion control given the very low viscosity of some MIMmaterials. In one implementation, for example for a MIM material whichbegins to melt or liquefy at around 130-150 C, the material may beheated in the print head to 180-230 C to promote adhesion. In thisalternative, instead of reducing the volume of the melt zone using along, thin melt channel (e.g., 1:10 width-height aspect ratio fordiameter and a volume of 20 mm{circumflex over ( )}3, the melt zone maybe a short 1:2 aspect ratio and a volume of 20 mm{circumflex over( )}3—e.g., 3 mm of melt zone height, 1.5 mm of melt zone diameter. Thelonger, thin melt channel however allows more heating length forexposure to a heating element (e.g., as shown in the Figures, a shortmelt zone cannot necessarily accommodate a large and powerful heatingcartridge). A reduced filament diameter (e.g. instead of a customary 3mm or 1.75 mm, a 1 mm diameter filament) may permit a smaller bendradius for a given temperature, and better control over an amountextruded—for a given step size on the extruder, less material isextruded.

With respect to advised or advantageous dimensions, below a 10:1 nozzleto particle diameter ratio jamming may begin. Jamming is exacerbated byless spherical particles (e.g., platelets or flakes, which can becreated during mixing or screw extrusion). Traditional MIM (or CIM)materials may be between 55% and 65% metal (or ceramic) powder loadingby volume, but at this level of loading, separation layer material insmall powder sizes (e.g., less than 1 um diameter) of alumina ceramicmay tend to sinter at steel sintering temperatures. As the size ofpowder increases slightly to 2 um, the separation layer may becomechalk-like. Accordingly, 15-35% powder by volume with a powder diameterof 5 um or higher for alumina or similar ceramic powder loaded in a MIMbinder (e.g., wax-polyethylene, as discussed herein) may perform well asa separation layer. Alternatively, 10-20% powder by volume with a powderdiameter of 2 um or lower (or 1 um or lower) for alumina or similarceramic powder loaded in a MIM binder may perform well as a separationlayer. Further, these may be combined (e.g., some particles smaller than1 um and some particles larger than 5 um).

A conventional FDM/FFF filament or melt chamber may be approximately1.7-3 mm, and in the present invention the melt chamber may be 0.6-1 mmin diameter for a tip outlet diameter of 0.1-0.4 mm (for a filamentdiameter of 1.0-2 mm). The volume of the melt chamber (the heatedsubstantially cylindrical chamber of constant diameter extending fromadjacent the nozzle tip to a melt interface) the may be approximately15-25 mm{circumflex over ( )}3 vs. a melt chamber in conventionalFDM/FFF of approximately 70 mm{circumflex over ( )}3.

As shown in FIGS. 38A and 38B, an FDM/FFF nozzle assembly may include anozzle 38-1 including part of the cylindrical melt chamber 38-2 having alarger diameter and a transition to the nozzle outlet 38-3. Thetransition may be smooth (tapered 38-4, as in FIG. 38A) or stepped 38-5(as in FIG. 38B). Both the nozzle 38-1 and a heat break 38-5 aretightened (e.g., screwed) into a heater 38-6 block to abut one another,the heat break 38-5 including the remainder of the cylindrical meltchamber. The heat break 38-5 includes a narrow waist made of a lowerheat conductivity material (e.g., stainless steel) to provide the meltinterface via a sharp temperature transition between the top portion ofthe heat break 38-5 (which is cooled via the heat sink) and the lower,conductively heated portion of the heat break 38-5. The melt interfacebetween the solid filament 38-8 and the liquefied material in the meltchamber 38-2 is typically near the narrow waist (adjacent above orbelow, or within). As shown in each of FIGS. 38A and 38B, an FDM/FFFnozzle assembly may include a melt chamber of approximately 1.8 mmdiameter and 10 mm height, a volume of about 70 mm{circumflex over( )}3, vs. a nozzle outlet of approximately 0.25-0.4 mm diameter. Asshown, a cartridge heater 38-6 (in FIG. 38A) or a coiled inductiveheater 38-6 (in FIG. 38B) are suitable. As shown, in some cases a PTFEinsert 38-9 may provide resistance to filament jamming.

As shown in FIGS. 39A and 39B, a MIM material extrusion nozzle assemblymay be structurally similar—e.g., with a smooth or stepped transition inthe nozzle 39-1, a heat break 39-5 including a narrow waist, and othercomponents as previously described (e.g., with reference numbers 39-#corresponding to numbers 38-# previously employed). A solid-statePeltier cooler may be used on or adjacent the heat break 39-5, and maybe adhered to the heat break 39-5 by heat transfer cement or other highheat conductivity interface. As shown in each of FIGS. 39A and 39B, aMIM material extrusion nozzle assembly may include a melt chamber 39-2of approximately 0.6-1 mm diameter and 10 mm height, a volume of about20 mm{circumflex over ( )}3, vs. a nozzle outlet 39-3 of approximately0.1-0.4 mm diameter. As shown in FIG. 39B, a narrowing insert 39-11 maybe used to convert an FDM nozzle for MIM material extrusion (e.g., themelt chamber volume vs. nozzle outlet size or filament relationshipsdescribed herein are related to MIM material dimensions duringextrusion, not necessarily the specific nozzle, heat break, or insertparts). As shown in FIG. 40, a MIM material extrusion nozzle assemblymay include a melt chamber 39-2 of approximately 1.7-3 mm diameter and1-4 mm height, a volume of about 20 mm{circumflex over ( )}3, vs. anozzle outlet of approximately 0.1-0.4 mm diameter.

With respect to the binder jetting example shown in FIG. 1B, in all ofthe preceding examples in which an extruder using filament is notrequired, the binder jetting example printer 1000J and associatedprocesses may be used. In a 3D printer for making desired 3D greenparts, a binder may be jetted as a succession of adjacent 2D layershapes onto a sinterable metal or ceramic powder bed in successivelayers of powder feedstock, the powder bed being refilled with new orrecycled feedstock and releveled/wiped for each successive layer. The 3Dshape of the desired 3D green part and associated sintering supports orunderlying shrinking platform (for holding unsupported spans of the 3Dgreen part in place vs. gravity during sintering and maintaining anoverall shape of the 3D green part) are built up as a bound compositeincluding the sinterable powder and the binder, embedded in a volume ofloose powder. The 3D green part and its sintering supports will later bedebound and then sintered, and the sintering supports removed.

In some layers, differing amounts of binder may be jetted depending onwhether a 2D layer shape segment being formed is an external wall,internal wall, or honeycomb wall, or internal bulk material (ordepending on the printing location relative to such perimeters orareas). This results in differing (optionally a continuous or stepwisegradient) of volume fraction proportions of binder to powder, e.g., from90% binder to 100% powder through 50:50 up to 10% binder to 90% powder.For example, a higher volume fraction of binder may be located on anouter shell (and/or inner shell), progressively reducing inward toward,e.g., area centroids.

In some layers, a release material (including another powder that doesnot sinter at the sintering temperature of the feedstock powder) mayalso be applied in a complementary 2D shape (e.g., jetted in a binder,extruded in a binder) for example, intervening between a support shapein a lower layer and a part shape in a layer two above.

In some layers, placeholder material (without either the green partpowder or the release material powder) may also be applied in acomplementary 2D shape of desired free space within the green partand/or sintering supports (e.g., jetted or extruded). In some layers,the placeholder material may also or alternatively be applied in a wallor “mold” shape, e.g., occupying external free space to the part shape,capturing unbound sinterable powder inside the mold shape. In otherwords, an external shell (e.g., wax) may be formed of the placeholdermaterial. The external shell 2D shapes are deposited in each candidatelayer on top of the preceding powder (e.g., bound powder, unboundpowder, and/or release material) layer, then a subsequent layer ofunbound powder feedstock is wiped on. As shown in FIG. 1B, a doctorblade 138 may be used to slice the top of the 2D shell shape off(leveling) or a silicon roller/blade 138 may be used to slice the top ofthe 2D shell shape off—the silicon roller/blade may accept somedeformation, e.g., deform to accommodate the bump of the plastictolerance above the printing plane.

The binder may be jetted into roofs, floors, lattice, honeycomb, orskeletal reinforcement shapes within the mold shape (e.g., startingspaced away from the mold shape) to help hold the unbound sinterablepowder versus gravity, or mechanical disturbance during downstreamprocesses such as leveling or moving the part from station to station.For example, in some 2D layers, an internal holding pattern such ashexagon, triangle, or as previously describe lower density or highvolume fraction of binder may be used as a holder, in combination witheither an outer shell formed from bound composite, an outer shell formedfrom high volume fraction binder bound composite (e.g., 70% binder),and/or a mold shape formed from the placeholder material. As noted, thismay help prevent motion of parts during printing/or during layerre-application.

Further, in some layers, the placeholder material may also oralternatively be applied in a complementary 2D shape of adhesivebetween, e.g., the shrinking platform formed from bound powder and theunderlying build platform, or between a plurality of adjacent or stacked3D green parts and associated sintering supports to allow multiple partsto be built up per run. The adhesive function may, again, help hold theany of the shapes versus mechanical disturbance during downstreamprocesses such as leveling or moving the part from station to station.It should be noted that the binder jetting into sinterable powder mayalso be used to form adhering tacks as described herein between theshrinking platform and build platform, as well as or alternativelybetween a plurality of adjacent or stacked 3D green parts and associatedsintering supports. In other words, the part may be anchored part with(e.g., solvent removed) binder to a ground plane (e.g., build plate)and/or parts to each other (e.g., in the Z axis, when printing one ontop of another).

After each layer, the powder bed is refilled and releveled/wiped (with adoctor blade 138, roller, wheel or other powder leveling mechanism)flush with the green part shape, the release material shape, and/or thefree space placeholder material shape. Optionally, a surface finishingmechanism flattens or shapes (rolling, shaving, ironing, abrading,milling) a recent or a most recent layer of green part shape, releasematerial shape, and/or placeholder material shape before the powder bedis refilled about them.

The 3D shapes of each of the green part, sintering supports, interveningrelease material, and placeholder free space material are built up insuccessive layers, and in 3D space may take essentially any interlocking3D forms. In many cases, the green part is formed as a recognizable 3Dobject, with separation material forming planes, arches, hemispheres,organic shapes or the like separating the 3D object from columns ofsintering supports below, leading down to a shrinking platform asdescribed herein, which is adhered to a build platform via placeholdermaterial and/or bound composite tacks. Optionally, as described, withinthe recognizable 3D object, desired free space may be filled withplaceholder material and/or unbound sinterable powder. Among theplaceholder material and/or unbound sinterable powder may be depositedbound composite honeycomb or lattice or the like containing orentraining either or both of the placeholder material or unboundsinterable powder. Optionally, as described, about the recognizable 3Dobject, a mold shape defining the outer skin of the 3D object may beformed of the placeholder material. Additionally, or in the alternative,a skin shape forming the outer skin of the 3D object may be formed ofthe bound composite.

Subsequently, the 3D green part(s) together with sintering supports,release shapes, and placeholder or adhesive shapes is removed from thepowder, and cleaned of remaining unbound powder. Unbound powder may beremoved from the surroundings of the 3D green part(s) and sinteringsupports via outlets formed in the bound composite, or left entrainedwithin the desired green part. Subsequently, the green part and itssintering supports may be handled as otherwise described in thisdisclosure. Bound composite outer and inner walls and internal honeycombwalls will be debound as described to form the brown part assembly.Release material will be debound as described, become separation powderfor removing the sintering supports, and is retained for sintering andremoved following sintering. Placeholder material may be debound(including in a solvent, catalytic, or thermal process) or even, if adifferent material from the binder, removed before or after debinding.In some cases, high temperature placeholder material that retains itsshape at high heat but may be disassembled by further vibration,mechanical, radiation, or electrical processing (e.g., carbon or ceramiccomposite) may be retained through sintering.

Alternatively, the debinding step may not be necessary, for the greenpart shape and/or sintering supports if a single stage binder can bepyrolized in a sintering furnace. In such a case, the green partassembly is taken directly to the furnace. Bound composite outer andinner walls and internal honeycomb walls are debound and sintered in anintegrated process. Release material may be debound prior to theintegrated debinding and sintering in the furnace, or at may be deboundin the furnace as well. Placeholder material may be debound (includingin a solvent, catalytic, or thermal process) prior to the integrateddebinding and sintering in the furnace, or at may be debound in thefurnace as well.

A material may be supplied (pellet extruded, filament extruded, jettedor cured) containing a removable binder as discussed herein (two or onestage) and greater than 50% volume fraction of a powdered metal having amelting point greater than 1200 degrees C. (including various steels,such as stainless steels or tool steels). The powdered metal may havewhich more than 50 percent of powder particles of a diameter less than10 microns, and advantageously more than 90 percent of powder particlesof a diameter less than 8 microns. The average particle size may be 3-6microns diameter, and the substantial maximum (e.g., more than the spanof +/−3 standard deviations or 99.7 percent) of 6-10 microns diameter.

Smaller, e.g., 90 percent of less than 8 microns, particle sizes maylower the sintering temperature as a result of various effects includingincreased surface area and surface contact among particles. In somecases, especially for stainless and tool steel, this may result in thesintering temperature being within the operating range of a fused tubefurnace using a tube of amorphous silica, e.g., below 1200 degrees C.Smaller diameter powder material may be additively deposited insuccessive layers to form a green body as discussed herein, and thebinder removed to form a brown body (in any example of deposition and/ordebinding discussed herein).

Definitions

A “sintering temperature” of a material is a temperature range at whichthe material is sintered in industry, and is typically a lowesttemperature range at which the material reaches the expected bulkdensity by sintering, e.g., 90 percent or higher of the peak bulkdensity it is expected to reach in a sintering furnace.

“Honeycomb” includes any regular or repeatable tessellation for sparsefill of an area (and thereby of a volume as layers are stacked),including three-sided, six-sided, four-sided, complementary shape (e.g.,hexagons combined with triangles) interlocking shape, or cellular.“Cells” may be vertical or otherwise columns in a geometric prism shapeakin to a true honeycomb (a central cavity and the surrounding wallsextending as a column), or may be Archimedean or other space-fillinghoneycomb, interlocking polyhedra or varied shape “bubbles” with acentral cavity and the surrounding walls being arranged stacked in alldirections in three dimensions. Cells may be of the same size, ofdiffering but repeated sizes, or of variable size.

“Extrusion” may mean a process in which a stock material is pressedthrough a die to take on a specific shape of a lower cross-sectionalarea than the stock material. Fused Filament Fabrication (“FFF”),sometimes called Fused Deposition Manufacturing (“FDM”), is an extrusionprocess. Similarly, “extrusion nozzle” shall mean a device designed tocontrol the direction or characteristics of an extrusion fluid flow,especially to increase velocity and/or restrict cross-sectional area, asthe fluid flow exits (or enters) an enclosed chamber.

“Shell” and “layer” are used in many cases interchangeably, a “layer”being one or both of a subset of a “shell” (e.g., a layer is an 2.5Dlimited version of a shell, a lamina extending in any direction in 3Dspace) or superset of a “shell” (e.g., a shell is a layer wrapped arounda 3D surface). Shells or layers are deposited as 2.5D successivesurfaces with 3 degrees of freedom (which may be Cartesian, polar, orexpressed “delta”); and as 3D successive surfaces with 4-6 or moredegrees of freedom.

In the present disclosure,” In the present disclosure, “3D printer” isinclusive of both discrete printers and/or toolhead accessories tomanufacturing machinery which carry out an additive manufacturingsub-process within a larger process. A 3D printer is controlled by amotion controller 20 which interprets dedicated G-code and drivesvarious actuators of the 3D printer in accordance with the G-code. “Fillmaterial” includes composite material formed of a debindable materialand a sinterable powder, e.g., before debinding.

“Fill material” includes material that may be deposited in substantiallyhomogenous form as extrudate, fluid, or powder material, and issolidified, e.g., by hardening, crystallizing, or curing. “Substantiallyhomogenous” includes powders, fluids, blends, dispersions, colloids,suspensions and mixtures.

“3D printer” meaning includes discrete printers and/or toolheadaccessories to manufacturing machinery which carry out an additivemanufacturing sub-process within a larger process. A 3D printer iscontrolled by a motion controller 20 which interprets dedicated G-code(toolpath instructions) and drives various actuators of the 3D printerin accordance with the G-code.

“Deposition head” may include jet nozzles, spray nozzles, extrusionnozzles, conduit nozzles, and/or hybrid nozzles.

“Filament” generally may refer to the entire cross-sectional area of a(e.g., spooled) build material.

What is claimed is:
 1. A method of additive manufacturing, comprising:maintaining a first spool of a build material filament in a chamber, thebuild material filament comprising a matrix including one or more bindercomponents and more than 50% by volume of sinterable powdered metal;maintaining a second spool of a release material filament in thechamber, the release material filament comprising a second binder and apowdered ceramic; dropping the build material filament over a dropheight in the chamber from the first spool to a print head assembly;dropping the release material filament over the drop height from thesecond spool to the print head assembly; directly heating, with heatedair from a heater in the chamber, the build material filament on thefirst spool and along the drop height to a temperature lower than aglass transition temperature of a softening component of the one or morebinder components to flex the build material filament; depositing layersof the build material filament and the release material filament above abuild plate, the drop height being substantially equal to or longer thana diagonal of the build plate; debinding at least one of the one or morebinder components in the matrix and the second binder with a solvent toform a brown part assembly including each of the build material filamentand the release material filament; and sintering the brown part assemblywhile decomposing the release material to a release powder.
 2. Themethod according to claim 1, wherein the build material filament droppedalong the drop height has a bend radius of more than 10 cm.
 3. Themethod according to claim 2, further comprising heating the build plateby a build plate heater to 50-120 degrees C.
 4. The method according toclaim 2, further comprising: positioning the build plate below the dropheight; heating the build plate; and providing heated air from the buildplate to the chamber.
 5. The method according to claim 4, whereindirectly heating the build material filament on the first spool andalong the drop height includes drawing, with the heater, the heated airfrom the build plate into the chamber.
 6. The method according to claim1, wherein the one or more binder components includes a polymer inaddition to the softening component, and the softening componentincludes a solvent-extractable non-polymer component selected from awax, a fatty acid, a fatty acid ester, a fatty alcohol, an alkane, apetrolatum, a naphthalene, a glycol, and a glycerol.
 7. The methodaccording to claim 1, further comprising: laterally transporting theprint head assembly to traverse a print area of more than 50% of thesurface area of the build plate, so that the build material filament isunwound from the first spool by the lateral transporting of the printhead assembly.
 8. The method according to claim 7, further comprising:guiding the build material filament with a flexible Bowden tube leadingto the print head assembly, the flexible Bowden tube being less than ⅓of the drop height.
 9. The method according to claim 1, wherein thebuild material filament cross sectional diameter is more than 0.5 mm butless than 2 mm.
 10. The method according to claim 9, wherein a crosssectional diameter of the build material filament is equal to or lessthan substantially 1 mm, and the temperature is greater than 40 degreesC.
 11. The method according to claim 9, wherein the temperature isgreater than 50 degrees C. and less than substantially 55 degrees C.